Okay, I'm also going to take a stab at this, though to be honest I don't know why.
* Oil brand:
You bring up a lot of different brands and also mention things like "XYZ oil is cheap and bad" or "Pennzoil used to have wax", etc. Let's simplify this for you. All the big name oils are good (Mobil, Pennzoil, Valvoline, Castrol, Quaker State, Shell, Havoline, Chevron, Kendall, Warren, etc.), seriously they're all good. Now some people might feel that one oil is better than the other, or one is a better value, but the fact of the matter is none of them are going to cause anything or allow anything to happen that one of the other oils would've prevented.
Your first post says you have Pennzoil Platinum (PP), Pennzoil conventional (PYB...it stands for Pennzoil Yellow Bottle), and Chevron (Chevron). All of them are excellent oils, all of them will protect your engine just fine.
Don't over think it, just stick with a name brand oil until you know more about the smaller oil companies.
* Oil Type:
As for if you should use synthetic or conventional, do some research on here and you'll see that conventional oils protect your engine just fine. Dino oil has gotten to the point where it protects basically just as well as synthetic oils. Where synthetic oils shine are in the extremities (extreme heat, extreme cold, extreme abuse, longer oil change intervals, etc). But for normal weather conditions, non-excessive abuse, and normal oil change intervals, conventional oil protects engines just as well. Since you're doing such short oil change intervals (OCI), conventional oil would work fine for you (even in Michigan winters). But this is an oil forum, so of course you'll see people arguing oils, or obsessing about oils, or using synthetic even though they know conventional oil would protect their vehicle just as well (I'm guilty of that).
So use either one. If using synthetic makes you feel better, then do that. If you want to save a few bucks, use conventional. You have a normal (non-turbo) engine, it doesn't sound like you do anything crazy with it, and you live where the weather conditions are pretty normal, so either one would work for you.
* Oil Weight:
Stick with the 5w-30 that your vehicle manufacturer suggested. Until you know better to make the decision on your own, do not use 5w-20 simply b/c someone else said you could.
If you want to use a 0w-30 you can. The first number being lower just means it flows better at cold temperatures, but it's still a 30 weight oil (the second number) at operating temps, which is what your manufacturer specified.
Do not expect any noticeable gains in gas mileage simply because you switch to a 0w oil. Yes, you can get a very minor improvement, but it's generally not noticeable, and it's only until the oil gets up to operating temperatures.
* Oil Change Intervals (OCI):
Until you know why you're deviating from it, stick with what your manufacturer recommended. Yes, most motor oils can go longer than that, but don't make a change on a whim. First learn about oil and understand why oil can last longer, then extended it out based on that, you can also get Used Oil Analysis (UOA) done which is where you send a sample of your used oil to a lab and they tell you the condition of the oil which will also tell you if it can be used for longer than you're running it.
It sounds like your OCIs are around 3k miles, which pretty much all modern oils can do easily. This is why I suggest checking your owners manual, because if it says you can do 5k or 7k mile OCI, then you might as well extend it out past 3k miles.
* Overfilling Oil:
In your engine, it's okay. Don't let it be excessive or anything, but if it's a half quart over, it shouldn't cause any problems. Same with being a half quart low. It's very important to note by "half quart low" I mean having the oil be a little under the Full line, but still well above the Low line on the dip stick.
Because of how it works, this is not the same on transmissions. You want to be as close to the proper level on your transmission as possible.
*Oil Filters:
You have a lot of questions about oil filters, and again were saying that some were bad or some were good. Similar to motor oil, stick with the name brands and you should be fine. Like when you said something to the affect of Fram orange cans are bad, it's not that they're bad. There are millions of cars driving around with Fram orange can filters and none of them are having problems because of it. When people bad mouth something like a Fram orange can, if you dig down into what they're saying, they're usually saying that for the price (or just slightly more) there are other filters that they feel offer better filtering and are therefore a better value.
You asked a lot of questions about filters, and the possibility of using the same filter across both your vehicles. I don't know if you'll be able to do that, but if you stick with name brand filters that are appropriately spec'ed for your vehicle, you'll be fine. Some oil filters that I like are Purolator (I use PureOnes), and Wix (or Napa Gold). Also the Fram Ultra line seems to be really good too. Don't get me wrong, there are a ton of good oil filters out there, but those are the ones I tend to stick with.
Side note on Purolator: As you read through this site you'll see that there have been a recent rash of Purolator filters having media tear issues, meaning that some unfilter oil was constantly going through the filter. I really like Purolator filters, but I've temporarily stopped using them until I see the issue has been resolved. It's nothing to freak out over, I simply will use a couple Fram Ultras or Wix filters until we stop hearing about media tears.
* Engine Flush:
Don't do it. Look at your owners manual and the manufacturer suggested maintenance. No vehicle manufacturer suggests an engine flush. As long as you're taking care of your engine, and doing oil changes at a reasonable OCI, then there's no reason to do a flush. In fact some people advise against it.
The same goes for Transmission Flushes.
* Transmission Fluid:
You mention your transmission a few times. I personally believe in doing periodic drain and fills on the transmission with approve transmission fluid. I don't believe in transmission flushes, and I'm very strict about sticking with approve transmission fluid. Do not simply change your transmission fluid to a different fluid on a whim. Transmissions are very picky, and need the specified fluid type for a reason. So just because you heard one fluid was really good, does not mean it's okay to use it in your vehicle. Stick with the manufacturer recommended fluid type (Merc, Dex, etc).
* Jack and Jack Stand:
Just do some research online and read reviews, you'll quickly start to figure out what's a good price, what are good brands, and which have issues with them.
A very important note: No matter what anyone tells you, or what you think, *NEVER* get under a vehicle that's being supported by a jack. *ALWAYS* use jack stands when you're going to be under the vehicle. It's rare, but jacks do give out suddenly, and you don't want to be under the vehicle when that happens.
* Power Steering Fluid:
Some, possibly most, manufacturer's say to use ATF fluid in the power steering (PS) pump. Follow what your owner's manual says, but don't just go putting fluids in, make sure it's the spec that your vehicle manufacturer says. I find the easiest thing to do, is periodically suck the fluid out of PS reservoir. Depending on your vehicle, you can do this with a small pump, or something like a turkey baster. I periodically pump it out and refill it. If I'm going to do it a couple times back to back to make sure I get most of the old fluid out, I take it for a quick drive and make sure to turn the wheels all the way in each direction before pumping it out again. This ensures that the fluid mixes, and that you're not just pumping out new fluid and replacing it with more new fluid.
* Spark Plugs and PCV valve:
You're coming up on 150k miles and you still have your original spark plugs and pcv valve? Personally, I'd look into how to change them and would make the change as part of routine maintenance.
