1) Each tag must be created in the AdminCP (Content Discovery > Tags). It's a bit like the current "closed" system where you have to add the tags manually if you want your community to use them.
2) No, this was a strong part in the new system; if it is going to work, it must be universal. To start omitting tags from some apps, some forums, etc weakens the entire system. This is a way to bring content across your community into one place. If you need tags like status labels (open, fixed, etc) then I would recommend a Pages database and custom fields.
Think of it like organising your house. You have a lot of things that can be hard to find (I know I had a charging cable here somewhere...) so you buy 10 large plastic crates and organise everything into those boxes (electronics, clothes, toys, cables, etc). You label each crate and it's now easy to find what you want. Need a charging cable? Open the cables box. Need to find your Gameboy (it's 1999 in my head) then go to the electronics box. It's easy.
If you then added a bunch of rules on top (blue cables can't go into any box, orange toys can't go into the toy box) then you break that simple and strong organisation.
Likewise, if you chose instead to buy 500 small lunchbox sized boxes and put one item in each, then you have changed nothing, objects are still impossible to find and are not in the same place.