Definitely a good idea! At minimum you want to test it without the computer but I do find that catastrophic failures on the old AT stuff isn't all that common.
The original fans are often very good. If replacing them you should use industrial grade fans, not consumer grade fans (like noctuas) especially if mounted horisontally.
Wurth Electronik. I also love the red color. I haven't had any trouble with them though sometimes they don't have the big high voltage input caps or they don't have the right physical size for that one and I end up with another brand for that one cap.
Might as well replace the varistor(s) while you are in there as they wear out too, and are quite cheap, just make sure you get the exact same value. Every spike they absorb wears them out a bit, so might be the first component to wear out.
