I don't have a '96, so YMMV...

The belt should be easy to take off. Maybe there's a tensioner pulley that's mounted on a little lever which pivots to tighten or loosen the belt. Alternator probably swings on its own mounts. Or maybe the PS pump slides on its mounts...

The crank pulley 'looks' like it's just one piece. But it's made up of a steel 'hub' which bolts to the crank. Then there's a layer (maybe 1/8" thick) of rubber. The pulleys are pressed onto that. It doesn't come apart; maybe the rubber layer is molded into place or something. If the rubber rots or gets loose, then the pulleys can wobble even tho their 'hub' is straight. That's what happened on my Jetta.

Take off all the belts. Then grab the pulley & try to wiggle it. If that rubber layer is OK, it should feel like there's no flex at all.

Engine mounts... I suppose you could grab your valve cover & try to rock the engine back & forth. It's supposed to flex, so it's gonna be hard to describe what's normal & what's not. You can see most of the mounts, so look for any rubber parts that are cracking or coming apart. Maybe there's a rear mount buried back under the firewall that's hard to see. I don't know if there's any one that's a more popular failure.

When it's idling with the AC on, watch everything as the compressor clutch engages & disengages. Is anything vibrating around? Watch closely, but keep your nose out of the electric fans....

This is gonna sound real stupid, but how's your tune-up stuff? The AC is by far the biggest belt-driven load, so when it engages at idle, it's maybe doubling or tripling the engine load. One spark plug that's a little dirtier than the others; or one plug wire that arcs just a little bit; might do it...