Your plants are looking great @perry2, keep doing what you are doing.
You should match your filter size to your exhaust fan size, a 4" system should be fine for a 4 X 4 tent. Be sure to provide for inlet air.
There are many different views on defoliation…My view is to not remove leaves unless they are causing some sort of problem. As I near the end of veg (last few weeks) I may remove a few fan leaves but mostly I tuck them under. In the last week of veg I may get a bit more aggressive with trimming. The important factor here is that the leaves are where most of the photosynthesis takes place. In effect, the leaves are the chemical factory the produces the food to fuel plant growth.
I am not sure how many plants you can grow in that space, I would think that you could grow at least four plants in there. It is largely dependant upon how large you want to grow them (ie how long to veg), this is assuming photos. Autos will be smaller by nature, I believe, I have never grown autos.
Most of them are. You have to consider cfm rating of the filter and static characteristics as well. 4" is merely the flange size, and can be a really big or pretty small filter.
You mean for the boards? That’s a little too big for the connectors. 18awg solid with high enough voltage rating is the best. A lot of hardware stores don’t carry it, need like an electronics store usually.
I wouldn’t sweat it too much at this point. If you’re going to spray plants, try to do so right at lights off. Just keep an eye out for more to pop up.