hi, sorry if these questions have been asked before, i'm having trouble finding the answers.

I just came back to the game after quitting at start of pandas. my main character was an orc deathknight that I had alot of transmog and achievements on, so i'd l,ike to keep playing him. problem is my friends are alliance, so i'll have to faction change him. I have a few questions

• if i'm on a different server to my friends, but same faction, can we still raid together? can we guild together? does it matter being in a guild?
• if i character boost my 90 deathknight with almost maxed engineering and mining, do i lose anything on him?
• i saw soemthing about artifact weapons. what are they, and will i miss out on cool story stuff if i do that?
• is there anything else to consider with my decision to boost this DK? I really dont want to lose transmogs or achievements. can i save whats in his bags at all?

thanks very much