If you're 5'7 for a road bike you're probably in the 50-54 cm range. In a mountain bike, you're probably in the 16" range.

If you're commuting on it mostly on road - you really don't need a suspension on it, at the most you want a front suspension.

If you want to ride on trails for fun, I'd say stay away from skinny road bike tires, you could swap thicker tires & tubes on to make it more comfortable - but given your price range, you really should buy about what you need and then upgrade the seat for comfort.