First grow planning!

Well hello all, I'm starting to plan my first real grow indoors. Im finally legal and couldnt be mor3 excited. I've never done anything huge indoor. Usually just veg. so I've got lots of questions I'm hoping I can get some answers for. I know the basics of growing so that's nothing new to me but I've always grown outdoors in the short Northern Michigan summers!
So i guess what I'm wondering is.
1. Pot size for grow tents is their a huge difference on 3 gallon and 5 gallon yield wise. I plan on vegging 4 to 6 weeks nothing to major.
2. Can I connect two 4x4x8 grow tents to 1 8" filter setup. The fan is HO an claims to pull out 920cfm. If so how would i go about that.
3. Which is the best 1000w or 600w. I've heard 1000ws aren't that much better then a 600w because the 600w is more efficient. Though I know the 1000w put out far more lumen and I know the more lumen the better. I'd have one per a tent!
4. Is promix a good soil, I like the idea of a soilless medium. Though I've heard alot of good about FFOF.
5. Does anyone run dehumidifiers the final 3 weeks of flower. Is there a noticeable difference.

 

I'm hoping to be somewhere around 25 to 30 plants. I have a 4x4x8 tent and a 8x4x8 tent right now. 2 250 6400k cfl lamps from apollo and still wondering about if I want to go with 2 1000w or 2 600w for the heat issues in the larger tent. I'll be picking up the ductwork next paycheck with my inline fans. . Cost is not a huge concern for me luckily haha, at the moment anyways. With that soil mixture do you add anything or let the nutes do the work? Promix is pricey but my friend keeps trying to push It and dutch master nutes.

 

Also 1 gallon just sounds way to small to me.. I was thinking 5 or maybe 7 gallon pots. But what do I know haha.