i had a bunch of 3.5 gallon buckets laying around so i used them in my vegging room. the plants arent big enough to fill the buckets early on in veg so i dont think itll hurt it that much. i gave them to a friend later on when i moved as he wanted to start up with the hobby and have since switched over to 5 gallons all around. i havent noticed a difference, but bigger roots = bigger plants.
with the net pots its there to keep the plants upright. the more hydroton there is in the netpot the stronger the foundation is for the stem of the plant. i have the standard 6" net pot lids right now, but i plan on switching to the 10" ones because if u grow trees, something that is almost a must with these DWC buckets, they sometimes tip over. i know that seems like a good problem to have, but its shocking to say the least when u walk into ur room and ur plants laying there, horizontal and helpless.