[Closed] Single speed set up tensioner and gearing

Hi all I am converting my first frame - alpine stars al mega d. Into a Ss to be used offroad. Can you throw a few suggestion re which are the top 2/3 SS chain tensioner devices that can take a beating without breaking apart and which Gearing You would go for .... I usually ride on Surrey hills but will race SS on the alps in September?

Thanks all !!!!