Depending on what personal and group gear you are carrying the size should not be an issue at all. I have run my 12.5' self support for a week with two people, no problem.
Think about the gear you will be carrying, it will help determine if you run a cooler and drybox or two coolers.
To add more storage space to your raft, consider lashing drybags on the left and right of your legs in the rowers compartment or adding a drop floor and attaching rocket boxes. Add side rails so add space to lash down ammo cans, first aid kits, etc. Cargo floor for the front and the rear for loading up gear and keeping it off the floor.
I attached a photo of a buddy's 13ft otter on a four day trip with one passenger. He easily had room to add another three days of food.
There are lots of old threads to get info on all of these options, feel free to continue the thread if you have questions...
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