Yeah hopefully. Should I do a full flush now or just leave it?
I doubt that you would have a sludgeing problem from a little of the recent universal green type coolant in with your red. The sludge issue was with the old-style Prestone green but that hasn't been sold for years. What will happen is it will compromise the long-life capability of the Toyota coolant as the anti-corrosion chemistries are antagonistic. So I would not leave it any longer than the 25-30k you would run with any normal cheapo coolant.
If you really want peace-of-mind, take the question to the BobIsTheOilGuy coolant forum, where they live and breathe HOATS, and OATS and ethylene glycol all day long. I think they'll agree with me.
On the other questions:
Toyota Red is best. Zerex Asian was a decent cheaper alternative, but only if you can get a good price, which it seems has been harder to do lately. You can get Toyota Red on Amazon.
Oil: I run SuperTech full synthetic at 6500 OCI. What I save on fluids I splurge on a NAPA premium oversized filter, the NAPA Platinum 41516 with synthetic media. I get Blackstone Labs UOA's every other change and they come back clean. I ran it once to 9000k just for chuckles and it still came back clean and even said I could go longer. But I prefer 6500-7000.
I have run unleaded regular since I brought her home in May of 1999. Never a knock, ping or misfire. Not once in 165k. I see no reason to run anything else without a S/C.
PS: Your favorite ATF. I use SuperTech.
Brake: Your favorite DOT 4. I use SuperTech.
I have a 5-speed. I run Redline MT-90 which is a synthetic GL-4. This is worth paying a premium for.
Diffs/TC: NAPA Synthetic GL-5 75w-90.
These are not performance cars. SuperTech fluids have good reviews on BITOG, give good value and are plenty adequate for the application.
A decent change schedule is WAY more important than the label on the jug.