I like the space the 14" provides. It is wide, but allows for easy frame manipulation. It also seems to work well with commercial stuff that is out there for when you must purchase something. But, that is just a vote; do as you wish.
I have done rabbets for the frame rests with both a router and table saw. That depends on what is available. I wouldn't do a block, but that also depends on what materials you have available.
My boxes made with butt joints are still in use after 5 years, but they have a tendency to get out of square. Just be careful in use since they don't hold up as well as the finger joints.