picked up a Giant Manitou today for next to nothing
It needs a new rear tire, so while I am at it I figured I'd askfor recommendations of some other upgrades that make sense. I have some cash I can invest to let me know your suggestions. My plan is to use it to put some miles on and get better at my fitness.
Your best bet is to ride it a bit after replacing the tire and decide from there. If you feel there is an issue with the shifting spend the money to fix that, if the brakes are not to your liking you can invest the money there, etc.
Generally the first things people change out are the contact points like grips, saddle, pedals for something that suits them best.