The 2.5L engine has the adjuster pulley mounted on a 'track' (ie bolt) and you adjust it tighter or looser by adjusting the bolt - the pulley will go up or down based on which way you go. I WISH it had that arm to make it easier. But a standard socket with a good extension makes easy work of this.
Note the pic:
IIRC, to loosen, lefty loosey. It will 'lower' the pulley. To tighten it back up, righty, tighty.
It is tight enough when you can press down on the long distance between the 2 top most pulleys and it gives less than 1" IIRC. Or if you have a belt tension gauge (I bet you don't), it should be between 140-160 lbs for a used one and 180-200 lbs for a new one.
If you start up the engine and it squeals like a stuck pig, it's probably too loose still.
As for fluids, I run full synthetics in my 97 SE.
Engine - Mobil 1 5w-30
Transmission - Redline MT90 (manual)
T-case - Mobil 1 ATF
Diffs - Valvoline 75W90 or 80w90 synthetic
It has run a lot smoother since I swapped that stuff in. I had 90k plus on mine when I made the swap.
For plugs, I run the basic 4412 Champions and they work very well. The only trick is getting the front-most plug out. If you slide the plug socket in there between the engine and a/c setup, you can pop it on. Then use one of those flex joints, then your extension. Easy to do w/o having to remove any additional parts.
I'd at least inspect the wires for wear or bad spots and replace if needed. Check the cap/distributor and since they are cheap enough, just go ahead and swap it for peace of mind.