>>1784376First, I would get the seatpost height situated with the rider. Why? Because judging by the headtube length, that frame looks pretty small for a 6'4" person. If you could get a tall enough seatpost and position the handlebar height comfortably for that person, then I'd say it's a green light to perform real work on that ride.
What should be done depends how much you're willing to spend. Oil chain (possibly replace since it's rusted, however if none of the links bind, it can stay), fresh brake pads, fresh tubes/tires, inspect sprocket and chainring for wear (replace if necessary), remove dork disk, index the shifting, remove the shitty seatpost rack (and optionally go with a real rack with proper mounting points), finally replace/grease all bearings. A very optional but more intermediate level and costly thing to perform would be to replace the fork with a rigid fork because suspension forks suck unless they're high end forks and even then, it's only needed off road, the replacement would preferably off a parts bike for money saving.
If you're not willing to spend much though, I'd just adjust seatpost height, handlebar height, index the shifting, oil the chain, replace brake pads, air the tires, remove the shitty seapost rack, and call it a day.
