First of all you need to apply here, if you get accepted then make sure you have subscribed to the steam addon collection (usually posted in the steam group announcements), then its just a case of checking when the next mission is planned and youre good to play.

Most of the time yes, it all really depends on who you want to play with, as long as they're ok with you playing with them

All donations currently go towards funding the clans server and keeping it up, any donation is very much appreciated but not mandatory.

The role you play such as grenadier or marksman is determined by your Team leader in the mission, you can request training missions if you would like to become a fulltime role for example a designated medic or AT rifleman, just get intouch with an admin