Yo dude, thanks for the detailed reply and is all interesting to hear cheers! It sound like you got ventilation sorted ok, as that fan is moving enough air to cover the size ok, and if you got negative pressure suck-in going on then air supply shouldn't be any issue. Like you say, possibly circulating over the colas may help abit next time, though from the sounds of how well you got it set it up, i don't think air supply/circulation is the issue causing smaller buds - sorry dude not to have answered it on that level!
Possibly though yes, light leaks may be responsible though i couldn't say for sure tbh, and only thing is i agree that yep it's good idea to double check is light proof for next time anyway.
Otherwise than that i guess you just chalk it all up to experience and still pulling the smokeable amount you did is a great result for first time still, so don't be too disheartened dude! You sound intelligent, committed and eager to succeed, so I'm sure you will - you've got the first grow under your belt already and the 2nd, 3rd, 4th,etc ones will all improve as you continue!