Assuming you have;
1) compression in the motor
2) spark from the motor
3) willingness to work at it
Then, it can be a good project.
Things you really need to be wary of though:
If it's sat too long, bottom end seal could go. It that happens, you're in bad shape. Tell tale sign is if it bogs down and will not clear out with low RPMs. Bottom end seals are not too expensive on these, but do require a fair bit of work.
Double check oil in the oil injector/the oil pump. Real easy for junk and rust to get inside the those tanks and create issues.
If you de-rust the tank (whatever method you use), make sure to then run an external fuel filter afterwards. Rust will continue to appear for a long time, regardless of the method you use (always parts left).
Since it sat outside, I'd spray some WD40 or similar lubricant down the spark plug hole into the cylinder. Even if the motor is not seized, that's a long time without oil going over that cylinder. Don't attempt to start it until you do that.
They are great bikes with a huge cult following. I have a 75 as well that has been converted to a motocrosser. Reliable as anything else I own and definitely more fun to ride than most. Simple to work on and any parts you need are available.
"The bold adventurer succeeds the best.” - Ovid
I drink the koolaid too...just not the orange kind.