New brake lines are good (nice to be able to stop)!

As long as you're replacing the fuel line go for 1/2" and install a good electric pump at the rear near the tank.

Most header mfgs will tell you they don't fit with column linkage, but it shouldn't be a big job to reroute the shift rod.

P/S is strictly up to you. How strong are you?

Two fours, carb size is going to depend on how "healthy" the engine is.

Keep in mind the Powerglide will not be as reliable as a T-400 in stock form. If your having a glide built, that's another story.