|Under A Bleeding Sun|
Iea who that is, but I'll give what advice I can. There are most likely far better ways to do this build (ranger comes to mind) but I'll stick with the hunter for this advice.
1) you can find the stag here. Its small size until level 4 where it goes to medium.size, therefore it can mever be a mount for a medium creature (ie you). You can speak with your gm about reskinning a different animal companion.
2) Mounted works best with small creatures(ie gnomes and halflings), though you can probably get away with it for archery, just be an archer first and mounted second. Your first feats should be point blank shot and precise shot. After that you'll want rapid shot, many shot and deadly aim. You'll need to throw in clustered shots and improved precise shot as well at higher levels. Archery without extra class feats is a somewhat long and painful road. The nice thing is you'll have much greater maneuverability.
Hey there, sorry to breathe life back into an old post but I was having this same issue with a game I'm currently in. There's a spell-less ranger in the party and we both really liked the idea of a stag mount, so what we ended up doing is just taking a horse animal companion, switching it's strength and dexterity, and naming it a "Great Stag." Does that sound like it works? It just seemed like the easiest thing to do.
A megaloceros seems to be exactly the kind of creature you're looking for, though you would need the undersized mount feat to ride it before 10th level, or 7th if you take boon companion.
If you're looking to re-skin something so you can ride right away, horse would do, though I would likely change the bite to a gore. I'd leave the stats the way they are, large creatures seldom have more dex than str.