Re: minn kota edge 40lb
No experience with that series but usually the release on MinnKota's is by pulling the corded handle. This releases the stowage lock and lifts the motor in one motion. Lifting it from the deployed to stowed position is the same way.
4, 1/4" bolts are plenty strong. Just use fender washers and/or a scrap piece of material to distribute the stress evenly over your mounting area. Also use lock-tite thread sealer or nylon lock nuts so they don't vibrate loose.
