Welcome and congratulations on the "new" old Invader. They are great sleds. Is that the complete serial number? A 79 Invader should be something like SS440A2-********.
Brake rotor wobbly - after 1100 miles, yes it will be wobbly, but that may not mean there is a problem.
Suspension will not travel - probably needs to be disassembled and serviced.
Crank seals - most definitely. Good crank seals and carb boots will make or break a good experience with this sled.
We have had Kawasaki sleds since the early 2000s. When we try to run them without checking them over inside and out, they generally don't run very long before a problem develops. Now we pull them all apart, check them out, and replace parts that are worn out of the service tolerance.
There are others on this site who have had these sleds much longer than I have who can probably give you some better advice.
Do you have a manual?