I agree with jb. When I got into Eurorack, I was looking at one 84hp rack, based on a free 3U space in my studio's 19" rack. Because of the advice here, I got a 7U 104hp rack instead. A few months later, it's now full. Get a Mantis (6U, 104hp) to start with. It's cheaper than the 7U and the 1U has far less choice in modules anyway. You won't regret going bigger.
-- Arrandan

thanks !