Fluid Change Intervals

Hi Folks I'm the happy new owner of an '05 Base model, 203,000 miles and I paid $4000 for it. Only issue thus far is the MFD screen, background colors will not go totally opaque and the background has a ghostly image like a railroad track or a guitar fretboard. All the functions still work and I can see it well enough, so at some point I'll be taking it out and sending it off to Upfit for a reconditioning since the free Youtube fixes of rubbing hard around the perimeter of the screen or tapping on it doesn't change anything (of course I'm open to other suggestions if anybody has them, and thanks.)

I plan to use the car only for once weekly commutes (highway driving) of 200 miles round trip, pretty much all highway miles. I bought this car specifically because I've been doing this drive 4 to 6 times a month for two years and my daily driver truck only gets 12 to 14 MPG...

I'm posting here for the camaraderie and community (which I very much appreciate since we live in Northeast Georgia, two hours from Atlanta and 30 minutes from Franklin North Carolina, and I really don't know if anyone near us knows how to work on these cars) and also because; there's what the factory and the manual says, and then there's what real world experience and ownership history says. I'm very grateful this forum is here and I appreciate the support, very much.

So, your thoughts; the most recent OIL CHANGE before I bought it was done with Valvoline 5W30 full synthetic, and my guess is that since there are no oil leaks (Seller only had the car three years) that it's OK to continue using a full synthetic oil. AND if the suggested oil change interval is 6000 miles, does it make sense to use Mobil One (the most expensive of the sfull synthetic oils) that CLAIMS it's good for ten thousand miles? This is what I chose to use at the first and all future oil changes in the RAV 4 Hybrid we got for my wife six months ago, and the manual says the oil change interval for that car is ten thousnd miles...

Since I don't know, and have no way to discover about it, should I;

Change the transmission fluid now, and then every 6000 miles, or more often?
Use the Toyota ATF, or is there a better one?

Just as a precaution, should I flush and fill the engine coolant now (and how often in the future?) And what pre-mixed anti freeze is best? (The inverter water pump WAS changed at 120,000 miles, I did find that reciept under the back seat when I cleaned it out)... And since it does have two water pumps and 203K miles should I attempt this myself or find a professional to do it?

MFD says the batteries stay at 14 volts yet I do not know if either of the two batteries are still the originals, leave them alone for now?

Brakes seem fine, leave them alone for now?

I've installed a K&N air filter, shall I keep burning regular (87 octane gas, or occasionally a tank of premium; hurts, helps, or waste of money?) Any opinions on an ocassional dose of Lucas fuel treatment? ("Chicken Soup" for cars right? Actually useful, or can't hurt?....

Tires are brand new and seem fine but are no doubt cheap off brands, SO next set of tires, same size? A size taller? Any suggestions for brand/model that last a LONG time? When rotating and balancing, always just swap front to back, or always X them so that aren't always turning in the same direction?

I can't think of anything else to ask about at the moment and I'm sure things will come up and I'll be back.
THANK YOU FOR BEING MY PARTNERS ON THE JOURNEY!!!