RE: First Rifle
If you're just getting back into it, I'd suggest you not get a powerful magnum cartridge of .300 or above.
In fact, I'd start with a .270 Win, .280 Rem, 7mm-08 Rem, .308 Win or .30-'06. All of these numbers will do everything you need and will not hurt so much at the range that you either develop a flinch or, worse, give up shooting again.
Once you've eased back into into it, you can get a big magnum if you think you need one....