But yes, chain tension is your challenge, make sure the frame has sliding dropouts, use a half link chain for the ability to adjust the tension in smaller increments.
Single speed MTB with a chain tensioner is also a hell of a lot of fun. This is mine:
Someone had a fun looking one on here a while back...
http://www.lfgss.com/conversations/273968/#comment12525905
But yes, chain tension is your challenge, make sure the frame has sliding dropouts, use a half link chain for the ability to adjust the tension in smaller increments.
Single speed MTB with a chain tensioner is also a hell of a lot of fun. This is mine: