Grammatically it could work. That depends on context though. Without context, (a) we can't tell if it works, and (b) it is actually meaningless. As soon as I read that, I thought 'in what way?'. Without saying in what way, I think it sounds a little inane.

The articles "a/an" are used for singular.

应该用复数

I would probably say "All things are beds of roses." or "Things are like beds of roses."