What's the procedure for new 270 win brass before reloading, full length resized or just neck resizing?

It would be best to FL resize as there can be deformities from shipping, manufacturing etc., but the most important spot is the neck.

Typically I will run them through a neck sizer to ensure round case necks. It probably doesn't really matter one way or the other. Most new factory brass isn't touched much, if at all, by a FL die except for the neck.

I go to a little more work than most, but I think its worth it.
1) If I want fifty cases I'll buy 100, and separate by weight.

2) put all selected cases into the tumbler and clean with corncob.

3) full length resize and trim to length of shortest case

4) deburr inside and outside of necks

5) recut primer pockets and deburr flashholes.

6) load and have fun.

BigBob - I agree with every thing you stated with the exception of cutting new primer pockets. The quickest way to ruin new brass is inadvertently enlarging the primer pocket by attempting to uniform the brass. If the primer pocket is questionable, I toss the brass. Everything else is easy to correct, however, I have yet to find a way to make primer pockets smaller.