Not sure what your thoughts are on ammo but things to consider.
Of the two choices you list...........
7WSM- Factory loaded ammo (Lots of choices there), factory brass, good availability, reloading dies are a little cheaper, great ballistics, possibly a little harder on the barrel, is going to use a little more powder to get velocities, more than likely you will get a good rifle right from the get go and not worry about rechambering, barrel, ect. This might leave the gunsmithing expense out of the overall price that could be spent on better quality optics, stock, whatever.
280AI- Only factory loaded ammo is from Nosler, same with headstamped brass otherwise you will have to fireform your own from standard 280 Rem (No real big deal just adds a few extra initial dollars and components), great round, I love mine, great ballistics, darn near reaches 7mm mag performance with less powder and recoil, not your everyday caliber.
One other thing, I also agree with others that advise to wait and get what you want. I tried to cut a few corners in the beginning and so far it has just cost me more in the long run.
Anyway that probably did more to muddy the waters than anything. Good luck, either would make a fine round that would do just about anything asked of it.