Go here for repair and maintenance tips: http://sheldonbrown.com/ and especially here: http://sheldonbrown.com/repair/index.html

Here is info on your one piece crank, aka Ashtabula. http://sheldonbrown.com/opc.html If you are going to go to the trouble of regreasing the bottom bracket, I'd replace the ball bearings, too.

I'd go with 27" wheels so you don't have to replace the brakes. Alloy wheels will be lighter and braking will be much improved.

I would replace the brake pads, the old ones are most likely hard as bricks.

Hopefully someone here can give you some tips on making those turkey levers work better. I don't recommend them but others say they are okay.

Good luck!