It's tricky buying a pack as a gift, between gear weight, gear volume, pack size, belt size, etc. +1 to what eric said about making sure returns/swaps will be hassle free.
Nice thing about getting a pack from REI, Backcountry is that he'd have a lot of other options for packs if he wanted to upgrade on his own dime. I know if it were me and a relative got me a new pack, tent, or sleeping bag I'd appreciate the thoughtfulness but it'd probably not be what I wanted. I don't know about your brother, but when someone gives me an almost-but-not-quite gift that I can't exchange/return it ends up in the closet.
Between the 3 lb bag and 4.5 lb tent, I would steer away from the ULA Conduit, Golite Jam, and anything else frameless. IMHO, the Mariposa Plus may work, but might not be the most appropriate. You can find the Nimbus Ozone within your limit, might be a better choice than the Vapor Trail.
Good luck, and I hope he loves it!
EDIT: +10 to what Mary said!