Will I still be able to get text messages from my favorites when I turn on Do not disturb?

No. Well, you will get them, but you will not be notified if the phone is in standby. DND silences ALL alerts other than phone calls from contacts you have designated as allowed through (and the alarm clock, of course).

I guess the only work-around would be to set the auto-lock to "never," which would be a BIG drain on the battery.

Which would also prevent DND from working. So you might as well turn DND off and let it go to sleep.