I hear ya on the where to start....and sorry. As mentioned, I've done a bunch of reading so I "know" the basics but where I am struggling is specifics. Since my cab is small, I obviously can't go with a 1.5 gallon (or I could but I think that I would have no room for flowering, but since I have no friggin clue, I dunno
I was hoping for a go with X tall, Y wide based on the measurements given. With 24" of height, I didn't want to run out of room but don't want to root lock either. On the soil, I'm thinking plain (non-Miracle Grow) potting soil mixed with 1/4 perlite and was hoping for a "you can find just about anywhere" plan B option.
Re: Ventilation - Your right, 2 pc fans. Passive intakes in the bottom with filters on them. The black that you see on the fans is cut to fit carbon filters (hardware wire on them to keep the filters from hitting the blades). I made it with the angled back on the cab to add a secondary pass layer of carbon on the outside (3 layers). If my calcs are right, I'll be changing the air 7 times an hour, even with the restrictions added by the filters.