I am not too familiar with the intricacies of legal formations. But based on the transfer priorities looks Like Fisch may be planning on running multiple RBs in formation.
Could we see the offensive version of Kwiatkoski Defense? With 2 Down lineman, 2 Tight ends, 6 WR/RB and 1 QB on the field at once? It's what our roster is built for.
You don't need 5 OL but it's the most advantageous to have 5 OL. A legal formation will have 2 ends on the LOS and 4 players in the backfield be eligible for a pass (includes a QB). You can always have less than 4 in the backfield but only the two on the outside at the LOS are eligible to catch a pass.
If you were to run an offense with 4 OL, one of the other position players would be required to be a blocker and cannot move downfield on a throw. Therefore, it's advantageous to have 5 OL since you have 5 dedicated blockers and 6 dedicated skill positions.