Determine Gender Before Going to BB's

Long time lurker, first post! This will be my 2nd grow room.

I am building a new grow space to be about 4ft x 2ft and hope to be growing a couple of plants at a time. I plan on growing by bubble buckets but I want to grow atleast 4 plants through veg to ensure I get atleast one female, then transplant to the BB's. Any advice on the best way to do this?

I was thinking about constructing a dwc rubbermaid (~20 gal) to start 5 plants but I am worried about the roots competing and getting tangled, making it very hard for the plants to live through a transplant.

I wouldn't worry about the roots getting tangled unless you plan on growing them there taller than 12 or 15 inches.

keylime