if i like and want to keep a bike, i do not use retainers for the bearings. i use loose bearings. in a normal bb that uses 1/4" balls in retainers, you fit two additional loose bearings on each side to spread the load a little more.
if it's a cheaper bike (a flip), using retainers makes it a little easier to install the bb.
if unsure about bearing size or count, look up the component on velobase. it's very easy to test bearing size and count by spinning the spindle in the dry cup full of bearings but without grease.
Yossarian: don't worry. nothing's going to happen to you that won't happen to the rest of us.