I'm in the same boat, I'm in the beginning stages of getting a base station setup to communicate (simplex) with my son 20+ miles away in the Dallas area; relatively flat terrain, but lots of homes, outdoor shopping centers, schools, etc. in between. We do have a repeater in-between us, but the idea is for simplex comms in case that is not an option. Basically two way emergency comms if "things" go south.
It looks like buying the best possible base equipment/ cabling/antenna system at both ends of transmission and actually trying it out is the only solution, since there is no real magic formula to this endeavor, nothing written in stone. I know someone here said they got 200 miles in distance, but I'll bet he doesn't live in the Dallas/Ft Worth metroplex.
If we fail in in direct two-way comms, we'll still have the repeater, plus each of us will have a bitchen' GMRS setup anyways. My other contacts will be within 11 miles and closer. And 20+ miles away is a gamble, a crap shoot, but a chance I'm willing to take.