One of the Members - I forget who - wisely said in a previous post addressed to Joanne, ...Plan on spending 25% of the purchase price on things you want to change/or add to it within the first couple of months..." or words to that effect.
He was RIGHT! I am almost up to that 25% amount now, and I have only had the plane (a 1975 Commuter) for 50 days!
It's fun, though, and you will enjoy putting improvements/ finishing touches on your plane.
So far, I have:
1.) Re-done the majority of the interior.
2.) Added big smoked plexiglass sun visors.
3.) Done a few peripheral minor powerplant mods suggested by my A&P - new high pressure oil hose, and a gas hose.
4.) Gotten a new rear window, and new carpet in the baggage area, only.
I have some other ideas, too, but I've about reached my spending limit for the pre-Xmas season - maybe next year.
The other guys have correctly answered all of your other questions.
Congrats and enjoy your new plane.