Welcome to Satellite Guys!
If you have DirecTV, then you know about rain fade, and that the dish has to have a clear line of sight (no trees, buildings, etc.) to the satellite! The same principle applies to FTA, except the signals are even weaker. So, that means a larger dish, and a different type of LNBF (the little circle thing on the end of the dish) because most FTA is broadcast on different frequencies than DirecTV. The programming isn't found on just one satellite, so having a motorized setup can be really nice!
There is Ku-band (using dishes about around a yard in diameter) and the C-band (using dishes 6 feet and up in diameter). Most of the English/network programming is on C-band (but if you're like me, you might not be able to put up such a large dish right now). Ku-band has a lot of foreign programming, but also a lot of sports and news feeds, which I like watching just as much as the regular channels. Setting up a Ku-band system gives you a lot of hands-on knowledge and is physically easier to move around
I'd first check
www.dishpointer.com and click on different satellites, particularly 125W, 101W, 97W, 91W, 83W, and 72W to see if you have a perfect line of sight to most, if not all of these, somewhere on your property.
If you find a good area for your dish, then go to The List at the top of the page (or Lyngsat), to get an idea of the kinds of stations you'll find on the air. If using Lyngsat, the lower frequency numbers (around 3000+) are C-band, the higher freq. numbers (around 10,000 and up) are Ku-band. Also check out the Beam column, which tells you whether or not the station is being beamed down to your area.
The big thing, which it seems you understand, is that FTA is no replacement for pay satellite TV (you won't find most of the nice premium channels for free out there), and that you cannot reuse the DirecTV dish for FTA (well some experienced people might, but I wouldn't try it!).
I'm sure someone has already posted, and you'll get lots of help here. Stick around, read the forums, and read the responses. Welcome to the hobby!