You have received a lot of good advice here; I'll add some thoughts. I have an 02 ES300 with the VVT-i version of this engine and have done a lot of work on it. It's at 240k and runs like a proverbial swiss watch.
As mentioned, the sludge issue on these is over-blown; it takes real neglect to get there.
a) Easily available/excellent quality/reasonable cost oil filters are in my mind either 1) Denso from the dealership (affordable, very high quality) or from RockAuto when you buy other parts, or 2) Wix branded or Napa Gold (same filter). Wix is in many major auto chains, Napa's are everywhere. Both filters are reasonably priced, very high quality, and good for 6 or 7.5k mile OCI's with quality synthetic oil.
b) I run ours on 5w-30 Mobil 1 High Mileage, from Wal-Mart cheap as mentioned. It LOVES it. Smooth, better power, slight MPG boost. I am now running 7.5k OCI's and it consumes about 8-12 ozs of oil in that period, after 240k miles on the engine. Remarkable.
c) The PCU will thrive on higher octane gas or even better yet, REAL gas (E0) if you can get it. Big MPG boost. I once splurged on a tank of 93 octane E0 and it was like a rocketship (relatively speaking). We got 30mpg with two adults, two kids, a trunk full of luggage and doing 80 mph on the interstate. This was with the next gen 5 speed tranny and VVT-I, but yours will benefit to the same degree.
d) A quality synthetic ATF in your PS system and transmission will make them last forever. MaxLife, Mag 1 synthetic, and others are great choices. Drop about 8 ozs. of SeaFoam in the AT a few days before the fluid swap to clean up the solenoids and valve bodies. Works great.
e) MAF Sensor, IACV, and PCV valve as mentioned.
f) there is a very good valve gasket DIY for this engine on Clublexus. com from a New Zealand member. I think his ID there is like ES300NZ. I'll try to find a link for you. When you do the valve covers, be sure to put in new 100k iridium plugs at the same time; you cannot access the back bank plugs w/o all that intake system off. I would not change the gaskets unless you find oil loss is noticeable or it is dripping. It is a PITA and if it's just a small weep, live with it until you need to change plugs or are doing the timing belt.
g) Don't neglect brake service; jack up each axle and spin each wheel by hand to make sure it moves freely without pins or pads binding. Try to rock it up/down and left/right to detect bad bearings. Then flush the brake fluid and get clean fluid in there and flush it every few years.
h) re: your starting issue. It's late here and I'm tired and not mentally in diagnostic mode. Make a post at Toyotanation.com in the avalon or the 4 gen Camry forum (same system, more eyeballs) and we'll work the problem for you.
i) when it comes time for suspension, the answer is KYB shocks and re-using OE springs and mounts (unless clearly failing). No Quick struts and no aftermarket mounts; unacceptably high failure rate with aftermarket strut mounts.
ClubLexus.com and toyotanation.com have a tremendous support group for owners. Keep in mind your drivetrain was not only in Avalons but in ES300s, Camrys, and the engine in RX and other Toyota crossovers, etc. LOTS of knowledge and support out there.
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At 232,000 miles (which I can't find pictures at the moment) it looked similar with only a bit more varnish.
The back bank at 299,000 miles looked like this:
and the underside of the back cover:
This engine has seen a steady diet of good quality (M1) synthetic oil changed out at an average interval of just around 7,000 miles. I replaced the rear cover at that point with the new upgraded one which uses the metal screw-in PCV valve:
The back bank on that engine gets much hotter than the front, at least in the Sienna version. I've had the exhaust off at various times to facilitate other maintenance and when you compare the mating flanges of both the exhaust manifold and the pipe, the rear one has much more heat damage and pitting than does the front. So that is why I said that if you are going to see a problem you are probably going to see it in the back bank.
