Chris
To do 35mm on the 57MB you will need a 75 or 80 mm enlarging lens. The bellows do not draw enough into the housing for a 50 mm lens. For medium format I use either an 80mm for big prints (11x14 and up) or my 135 mm for 8x10 & 11x14.
Do you have that aluminum insert for the negative carriers? With that insert all neg carriers for the Beselar 45MX will fit. I made a glass neg carrier for my 5x7 negs out of glass and mat board. You probably do the same for 4x5 negs.
If you have any other questions, just PM me as I have been using a 57MB for almost 20 years.
Good luck and have fun with it.