A 3 speed is totally doable for most commuting, including hills.
The freewheel compatibility for the S3X hub is related primarily to the style of the freewheel body. If the body has a "narrowed down" diameter inside the threaded area (a stop), then you cannot fully thread the freewheel onto the S3X and the chain line will not be correct. It took a bit of trial and error for me, but I found the cheapie "Dicta" brand to work well.