Does rackmount hardware attach only on the faceplate?
Yes, almost all rackmount devices are designed to bear their loads on the front plate. Only in very rare circumstances have I seen a piece of rack gear that has not remained rigid while mounted in a rack, and that was only after years of being in one. There are also some rack pieces that have a second set of mounts in the back, but I haven't seen that in a long time. 

My Crown power amp, which has got to be 50+ pounds, is only front mounted, as is my Akai S5000, which is about as unwieldy as it gets. You should be fine. Make sure you use four rack screws, and be careful not to overtighten them. You may also want to use rubber or nylon washers, but that's a whole other topic in itself.