My advise would be to go ahead and buy a lower and upgraded trigger now. No money is going to wasted there even if he changes his plans.
Here are some general thoughts on ARs, coming from the perspective that most companies put out quality products at this point in time, but a person can waste a lot of money of quality products that they don't need or don't benefit them very much...
Lowers: He can spend a lot or a little on a lower, but the two places that really distinguish a $50 stripped lower from a $400+ lower are the furniture and the trigger. Spending very much on a lower that has cheap furniture and a mil-spec trigger is a waste.
Barrels: Even an inexpensive barrel is going to be accurate enough to hit the kill zone of large game within the acceptable hunting distance for 223/300blk. The barrel is a component that most people associate with accuracy, but the real story is that accuracy is a combination of the barrel, ammunition, optic, shooter and shooting position. I could out shoot the best, most accurate AR in the world if I have a stable rest and the other guy is shooting free hand.
Optics: Here is an honest question, does he want to dial in shots or set the scope to one zero and then use a reticle and windage to shoot? Also, does he want to use one optic for one upper, or does he want to swap around optics and uppers? That's going to determine how much he needs to spend on an optic. A well built zoom lens, with good clarity, quality construction and pretty close adjustments cost a lot less that all of that with dead on, repeatable adjustments mounted on a quick detach mount that will hold zero when being re-attached.
Free float: At that budget, he might as well have it, even if it doesn't play a huge role in his shooting.