...All hoses should be replaced, coolant too. All fluids changed including brake and clutch fluids. The brake and clutch master and slave cylinders may need new seals. I would also change the o-rings on the coolant elbows under the carbs. Chances are the carbs will need to be cleaned and the carb rubber manifolds changed as well. Tires will need to be replaced as well. Fork seal will probably need to be replaced soon too.
The above is a very wise & thorough assessment. What needs to be understood is that there are a lot of items on vehicles that are calendar life limited, not mileage limited. This is because these components, most of which are rubber, perish over time. There is a greater risk of rubber components perishing on a vehicle that has not been used than on a vehicle that gets regular use, simply because the fluids on an unused vehicle don't get changed at regular intervals. This bike is 30 years old, brake & clutch fluids should be changed every 2 years, but it is doubtful that this bike has had 15 brake and clutch fluid changes.
My suggestion is that you research the cost of buying all the parts mentioned in
@bdalameda 's post, then, if you are willing to spend an enjoyable winter in the garage replacing all those components (plus a battery) and cleaning out all the old fluid systems (fuel, brake, clutch, oil, coolant), then go ahead and buy it. Otherwise, pass on it.
Apropos of that, I once went to assess a DHC-6 Twin Otter aircraft that was 40 years old but only had 800 hours flight time on it (between 30,000 an 40,000 hours would have been normal for that age of plane). Even though it had been stored in a hangar in a desert climate all of its life, and it looked like it had just left the end of the production line, my estimate was that it would cost slightly over $1,000,000 to make it airworthy again. None of the components on it had reached their cycle or flight hours limit, but every single component that was calender life limited was time-expired, and the engines required full overhauls because of concerns about internal corrosion that may have developed.
Having said all that, once the money was spent, the plane was literally "good as new"... but the money had to be spent first.
Michael