Are you sure you want to do your first ever trip, hiking 2.5 day's, carrying 5 gallons of water? That's 41.75 lbs. of water, before any other gear? Add another 7lbs for a tent and you're at nearly 50lbs, or 25lb each,not counting packs, bags or anything else, food, cooking gear, even your own clothing? Especially in hot desert like conditions? Have you considered doing something easier, learning your limits, and acquiring gear, and gaining the experience to determine the gear you want or need, which a good reference has already been mentioned in this thread?

You've got a while. Visit some outdoor gear shops, talk to experienced people, maybe your local gear shop has some "introductory" group trips scheduled, usually for a nominal fee. Many also rent gear, to give you a chance to try before you buy.

I'm not trying to deter you from anything, and not trying to be Mr. "doom and gloom", but with the info you provided, it sounds like a recipe for something bad going down, just to what degree can't be predicted. Err on the safe side, that's all.

Just my .02's

Good luck..and welcome to the sport

J.