I think #1 is the most important consideration: does he expect to be able to do much of the work himself? Paying a shop is going to be very expensive, and may be more $ than the bike is worth.
I suspect the bike's value in good cosmetic condition and running, w/no issues is going to be similar to that of a VMax. I put that value at $3K to $4K. A really pristine, low-miles one could be more, say another $2K to $3K. That would be to someone who's looking for just such a bike.
I am sure you can find people online who are asking $8K for a low-miles, well-cared for example. That isn't what I expect them to fetch for the run of the mill one.
Really, the same things you look at in a VMax, or any older bike, and especially one which hasn't been operable in years, applies here. We have many threads about this.
Is the engine 'frozen?' Time to remove the spark plugs and dose the cylinders and combustion chamber with ATF/Acetone 50/50% and let it sit for a few days, and then see if the engine will turn-over manually! Not on the starter!
Don't forget to adjust the DOHC valvetrain! Ha ha just kidding!
The brakes will probably need to be cleaned out, maybe the calipers disassembled and the master cyl's. too. Im too lazy to see if they're cable or juice for the clutch actuation. So, lube all cables, adjust the throttle so it snaps-shut, and isn't sticky. You don't want a WFO throttle stuck open.
Use of something like contact cleaner like De-Ox-It on all the plug-ins for the electrical system, clean grounds, a good battery. Check the bulb sockets for corrosion. Get all the lamps operational. The horn too.
Tires are probably 20 years old? But use 'em as rim-protectors until the bike is operational, and then spend the $ on new tires.
Get a good color-coded wire map to use for trouble-shooting.
The carbs need to be cleaned out, and exam of the gas tank, the petcock (if it has one, I suspect it does) and replacement of the fuel lines, once the gas tank is cleaned & returned to service. I like vinegar for removing rust 6% 'cleaning vinegar,' or greater, but DO NOT leave the petcock in the gas tank if you use vinegar to remove the rust! It will dissolve the potmetal that fuel petcocks are made from! Make a blank-off plate for the fuel petcock, or if it has a fuel sender.
You might get it to fire on old plugs, but spark plugs are cheap. Leave them out of the cyl head, ground them to the frame, and see if the spark plug wires and caps are allowing spark. Be sure the electronic ignition is grounded at each spark plug as they don't like not delivering their energy because they are not grounded. You could damage the CDI box.
Well, I think you get the point. Doing these things, you have a decent chance of seeing it back on the road. I'd say try to make the bike run, and then worry about everything else.
Don't get excited because you get the bike running before you do the throttle cable operation, the brakes, & etc sorted-out, and decide "oh, a short ride isn't going to hurt anything!"
You may be the proof that is not the case!
One of my friends had the 'pots & pans' GT750 2-stroke triple Suzuki, and it was as-fast as my H1.