Re: Manual Lenses
Press the Menu button and on the left there are several icons, go down to the second one (it's a C with a spanner) called the Custom Menu look for "Shoot W/O Lens" which is at the very end on "page" 5. Click it to "On". You can then forget about it because it won't affect the kit lenses, but it must be on for the camera to accept third party lenses such as your Pentax.
For manual focus assist press the left arrow then the Menu button in quick succession, it's clumsy at first but then you almost roll your thumb across the two buttons without hardly thinking about it. Remember to open up the diaphragm for precise focussing and then stop down to whatever you're using, otherwise you're focussing "stopped down" and apart from a darker viewfinder it's not going to be that exact.
Terry beat me to it. Naturally, she says "wrench" where I say "spanner" but you get the idea!