Day 4 update: Little Anita is growing slow and steady. The Fiji bottle is a bit taller than a solo cup, so I imagine it will be a few days before her roots reach the reservoir and growth takes off. She's starting to stretch out a bit so I turned on a few of the fans and lowered the light 1'. Never to early to start building strong stems.
looks good. i'd use a solo cup to start. anything over 500 ml is gonna take wks to catch. you could get half a grow in before it'd be set for up pot.
you want a third to half the media locked up and the roots well in to the res at up pot in hempy. the plants don't really get going until the roots hit the res.
5 gal is ambitious. a 5L (1 gal) bucket produces the same as an indoor 5 gal soil grow in hempy. 2 - 3 5L hempys should be sufficient to fill a 3 x 4.
i run a 4 x 4 and 5 5L is about all i can fit max. i normally run 2L buckets in hempy.
edit : also don't use anything but black or dark sided buckets and solo cups. perlite won't block the light, and a clear sided bucket or cup will severely slow and stunt growth.