The Redline is a heavier bike, but not crazy and lots of folks who have owned better bikes have plenty of praise for them still. Bet you could find one upgraded already or a used Monocog Flite in your price range.

I would lean to the SKM out of your choices just cuz I think it would do all the things you listed OK.

I converted a Rockhopper with the slider dropouts and like it alot, but it was more than your max. You might find one of the older ones on CL and build it up though.