Welcome!
Congrats on learning to change your own oil! Any good API SL, SM, or SN 5W-30 will suffice as long as you're changing it often enough. Valvoline MaxLife is a good suggestion, but personally I would use Quaker State Defy or Pennzoil High Mileage, or even the plain conventional Quaker State or Pennzoil (I'm a fan of Pennzoil/Quaker State oils). SuperTech (Walmart oil) is fine too, as are most of the parts store brands.
I really like Wix oil filters for your particular application, but Fram will work fine too. Fram Ultra filters would be good for 2x oil changes or 1 year, but I'd continue to change filters at every oil change while you still think you're having sludge issues.
If you are still having sludge issues, I would stick with 4 mo/4k mile oil changes. After a year or two you'll probably be able to safely extend that to 6 mo/6k mile changes. I like doing mine in April and October, when the weather is decent.
If you really want to extend your oil changes beyond 6 mo/6k miles, I highly recommend first doing a couple of normal oil change intervals with Pennzoil Platinum or Pennzoil Ultra (two of the best 'cleaning' oils in existence, in my opinion).
BTW, nice van! I enjoyed reading your other thread, it was informative and well written. Keep up the writing/blogging!