Wake-on-LAN is probably what you want, if your specific hardware supports it which it probably does. This is a case of figuring out your exact hardware and a little RTFM-ing about how to enable and use WOL.
As for the drives it, in theory, would add more load/unload cycles to them and thus reduce their lifespan. But, in the real world, that almost certainly doesn't matter, unless you're turning the system on and off every 5 minutes: modern drives expect to go in and out of power saving modes and most controllers (especially usb enclosures!) do this pretty aggressively, so a couple more load cycles more-or-less are unlikely to actually cause your drive to fail any quicker than it would anyways.