If this is a hobby then you can do this at your leisure. If this is project to make it road worthy in a short time then it needs to be budgeted in with the price of the bike. Either way, do it all and you will have an enjoyable, dependable ride.
if it rubber or if it's liquid, change it.
I would add that all up before the purchase to see what how much you will have in it when this is done. that plus purchase price will give you a picture of the bike and help you decide if it's worth it. It might also give you some leverage if you need the seller to come down a bit.
Timing belts are a biggie for most here. You can't look at one to know if it is good or bad. Your engine is almost instantly destroyed if these fail so best to spend the extra 50 or 60 bucks on those.
Squirting spray won't fix a bike that has sat for years, plan on replacing vacuum lines and a carb rebuild
good luck and take before and after pix, we want to see your progress
Hello and welcome to the forum.
If the bike sat for a long time may I suggest changing all the fluids, timing belts, fuel filter, good carb cleaning and syncing. A good service manual is a plus, get yourself the Honda Factory Service Manual or a Clymer. If you plan to go through the carbs may I suggest a kit from Randakks www.randakks.com the Goldwing Carb Specialist. Invest in a carb sync tool, it's a big help in getting all four to work together.