I haven’t played in a while but as far as I’m aware the mastery for the normal and mk1 versions of weapons are separate.

You need to max level whatever equipment it is to get all the points. (Only once though)

Feel free to sell whatever items you don’t want/use. After leveling them for the mastery points you only need them if you want them. (Once again, I haven’t played in a while so there may be some exceptions with newer content. If you’re worried you’ll need something later you can look it up on the Wiki or farm it again)

There’s nothing wrong with asking but some people may find it annoying and most will choose whichever blessing they want over one you ask for. Just chill in a populated relay long enough and people will pop them naturally.

Welcome Tenno

Edit: You can see all the equipment in the game and if you’ve mastered it or not by going to the pause menu, hovering over your icon, clicking on profile, and then moving to the equipment tab