I'm pretty much of a new guy, but not quite as new as you, so I'll offer my comments for what you may feel they're worth.
I, and my hunting partner, have made 3 trips to RSA, bowhunting only. I had a number of years rifle hunting in the USA before taking up bowhunting. Like 20 years, or so.
I'd suggest a frank and open discussion with you outfitter about the feasibility of his bowhunting opportunities. If you plan to hunt from a hide (surely a good options for the first trip) you'll want to know the distance from the hide to the bait/water. From what I've seen of bowhunting properties it's usually around 16 to 20 yards, but you need to know for sure.
As to the hides --- if the shooting ports are horizontal for rifle shooters, they may not work well for the bow. The bow hunting blinds that I have seen so far have shooting ports about 6" wide by anywhere from 12" to 20" tall. That much height is necessary because with you bow, the distance (vertically) may well be around 6" from your sight to your arrow on the rest.
We have hunted from pit blinds where as you sit in a chair your eyes are about ground level (does wonders for giraffe), ground blinds that the chair sits at ground level, elevated blinds that are much like Texas tower blinds, and "tree stands" that I would refer to as ladder stands.
No detail is too small to ask the outfitter well before your trip.
Having taken most of the regular plains game species with a bow, I can't imagine that the 308 wouldn't accomplish all that with ease, given the proper loads.
Seven days is pretty much "in and out". You won't believe how fast it goes by. Our first trip was 10 days, our second was 15, our third was 22. Each was too short. Yet you deal with what you can do. I've corresponded with a number of folks making they're first trip. I've not yet talked to anyone that didn't plan a follow on trip. So, be cautious there.
After our first trip I did a little write-up about things I wish I had known. I added a bit to it after the second and third trip. It too long to post here, but I'd gladly share it with you if I had your email address.
Best of luck with your trip and your choices.