Tent size questions.

Whats up, I've skimmed through forums for years for advice but this is my first time posting. I recently moved into a mobile home have an extra room I've decided to use for a little grow. I went back n forth on even growing at all since it's a mobile home and I've read there kinda shitty to grow in. But I've decided on going for it. My main concerns were smell since I'm in a park, and the electrical since it's an older trailer. I live in an area where it's pretty common and it is legal now so I'm not as concerned about that. And for the lights, I'm gonna keep it under 900w for now so it should be fine. My lighting will be a gavita 600/750, and I'm thinking about going with 6inch ventilation. My question is what tent size I should go with. The room is small, around a 6x8x7. I wanted to get a 4x8, start with one 600/750 and throw another in there beside it next run if my power could handle it. But I'm not sure if itd fit length wise. So I was thinking either a 4x4(and possibly get another depending on how it fits n room) or a 5x5 and just make the most of it. Would say one 600/750 in a 5x5 with 20 plants be enough light? Or just go with the 4x4 and throw 16 in it? Sorry for writing such a long post, wanted to give some background. Anyway any insights appreciated.

Also forgot to mention they'll be flowered pretty short, under a foot. Sog soil 3gal is what I'm thinking I'll do.

Never used Gavita but its typical to use 1000w DE for 5x5 , lot of people use them in 4x4 or 4.5x4.5

So with a 600/750 a 4x4 would be the most you want to cover.

Thanks for the reply man, I ended up leaning towards the 4x4 for now and possibly getting another later.