stoic, most groups are very friendly and will welcome new members. unless you are sure what you want to do, my advice is to attend several re enactments and talk to different people . there are infantry,artillery, cavalry, scout, communications, medical,and civilian re enactors.(and probably some i missed)!
somewhere in the neighborhood of 600 to 1000 dollars will get you outfitted to start with most groups. they try for authenticity and you can slip on a few things for a while, but if you stay , you'll spend a good deal more in time.
time commitment varies, but is usually several hours a month.(minimum)
thre are a number of publications that cater to re enactors.smoke and fire news, the camp follower's journal, north and south, blue and grey, civil war journal,etc.
rank is usually by election or appointment with group founders holding upper slots. (pretty muchlike it was then)
does this answer your questions?