Help with inner net material choice?

Denier can be used as a general gauge for fabric thickness/strength but it's not completely accurate. The denier refers to the number of fibres per square inch (I think) but doesn't say anything about the thickness of those fibres. That's why when you look at sheets the higher quality ones have a higher denier, in the 300 range. Sheets don't really get thicker so the higher the denier, the finer the fibres, the softer the sheet. Seconds nylon isn't reliably waterproof enough for a floor but the stuff from thru-hiker will be.

1.1 oz nylon should be fine for the sides. There are other nylons with better water repelancy like argon from dutchware or m90 from thru-hiker. The impetus from DIY gear supply is really good too.

Either netting would be good. I prefer the .7 because it's lighter but someone noted recently that it pulled more for them while sewing. I haven't found that but who knows. I will note though that .7 netting is always black. I've used it for baffles but not for a net tent. I've heard people say that a black netting tent is darker inside. Mine is grey but my new one will be black to save weight. Also, you can't mark black netting while sewing which is a pain. I've used painters tape in the past but it's another step that takes time.

Denier is a measure of linear mass of thread and yarn. It's the number of grams that 9000 meters of the thread weighs. (Nominally, there's rounding.) For a given fiber, lower deniers will thinner and lighter.

What you're talking about in sheets is thread count. Higher thread counts imply thinner threads, but it's more complicated that.

I expect the difference in weights is either someone is measuring coated and the other isn't, or they're very ifferent coatings, or the measurement(S) are plain wrong.

How big a project is making an inner net, I'm in the middle of my first project, making a cotton shirt to get some basic skills and will do a synthetic vest next.
Do I require a large working space to do this kind of project?

A bit of a sidetrack, but I just wanted to note that tailor's chalk (the clover stuff, not the waxy stuff) works decently on mesh netting. And thin slivers of soap work pretty well too (maybe even better, since they require less pressure to leave a mark).