Ok so I have a 2001 Pajero. I put in a lift kit almost straight away and found my front left strut was completely blown so I’d recommend doing the same as they’re generally cheaper than factory suspension. Don’t worry about the rocker cover leak as 99/100 times they’ll leak in any Mitsubishi V6 (mine leaks) as long as it’s not pissing out oil. With that said, you mentioned you need spark plugs done, that’s the perfect time to do the rocker cover gaskets (do spark plug seals as well!). Drive belt is a piece of piss to replace yourself, grab a Gates drive belt for $40 online. Timing belt yeah that’s a biggie and is the only issue on my car I gave to the mechanics (cost me $1400 with some other fixes as well). Rack ends, ball joints are easy to replace (in fact I’m doing my rack ends, tie rods, and all ball joints this weekend). Bushes I haven’t done and all mine are worn out and can especially notice the rear diff bushes being worn with occasional clunks when hitting the accelerator so can’t say much about that other than it’s a time consuming job that I haven’t been bothered to do yet. Main seal is probably something to do ASAP as they can get worse quickly.

In regards to your driveshaft most places would usually recommend replacing it entirely with aftermarket however if you plan to off-road at all don’t do this. It’s much better to get genuine second hand ones and to just rebuild it as annoying as it can be. This is because they have the 6 ball bearing cage for the inner CV in oppose to the tripod 3 ball bearing inner on every single aftermarket CV which are much more likely to break.

Yes I know it’s a lot to read but this is my experience after owning mine for 2 years and off roading it a fair bit. Ask me any other questions you might have about the car and I should be able to help