If the frame was made well then no extra prep will be needed. But I've seen FAR too many "good" frames with little or crappy facing and or needing chasing of the threads. One would hope that asking the source will get you an answer as to how prepped their frames are, but if this is a mail order or on line purchase you won't be able to touch/feel the frame first and bring it back when you find out that what they said wasn't totally correct.

As to the paint issue. I would remove the paint on the faces of the head tube and BB shell so no more paint chipping/flaking happens when you press/thread in the parts. It's not unheard of to have the paint on the end of a tube (the face) crush and flake off the tube with the force of installing the part. This flake can travel around the corner and into the exposed surface of the tube's length. I prep my build ups first by taking a small fine file (needle file) and holding it against the corner (45* to both the face and the length) just file through the paint. This cuts through the paint preventing any travelling of a chip past the corner. Then I use the same file and remove the paint on the face. Then I use the same file and lightly deburr the inside corner so to allow the part to slide past the face with no snagging (important with alloy headset cups). I'll chase, face and ream the head tube and BB shell also. But I have these tools so this costs me nothing.

An experienced eye can look at a frame and have a pretty good idea to the degree of after manufacturing finish prep that was/wasn't done. Pittsburg should have a few shops with the proper tools and skills. If a full ream, chase and face was needed it would cost around $20-40 each, depending on how well you are in with the shop (assuming a bare frame).

As far as the rust goes coat the insides of the HT and shell with grease. If the frame is steel then spray Framesaver or equivalent in it. Then once every year or two take all apart and repeat. Andy.