I have asked a friend of mine who is a great artist to paint something sweet on my telecaster.

so i was wondering what the process is like for taking the paint off the guitar, what i should do to make sure the new paint stays on well and all that?
As for a clear coat, get a can or two of nitrocellulose finish or lacquer finish from Reranch, spray maybe 30 coats or so for a nice deep gloss, and, if you pick lacquer, you have to let it cure and harden before you play it.
okay so first thing i would do is gradually sand it down to the wood... then what? do i apply the paint first and then the laquer/or nitrocellulose?

also, when painting and sanding the guitar should i remove and of the exterior parts or just cover them somehow?

how much do you think the total cost would come to?
You'll need to remove all the hardware on the guitar (including the neck), otherwise it will be too hard to sand around and underneath. Take some pictures before and you'll be good to go when you re-install them. You might be a bit worried about the electronics, but you should be able to snip a few wires (take pics before for later reference) to get the guts out or unsolder the connections. You'll have to resolder them but it's not as hard as it looks.

I've stripped a telecaster by using 60 grit sandpaper and a electric sander. I had tried paint stipper but no can do; that stuff is just too tough.

The only question I have is what kind of paint is your friend going to use? I'm wondering if the brush strokes (not sure type of painting your friend will do) will be really high/tall. If so, it'll take more than 30 coats to get it nice and even.