The FD's ('93 - '95) can be very finnicky in stock form. But there's a lot of mods that can be done to make it more reliable. The stock motor setup is very complex with the dual sequential turbo system and all the strange emissions controls and such.
Check out www.rx7club.com and look in the 3rd gen tech section to get an idea of things you can do, there's stickies at the top with tech details, and search reliability mods to get an idea of what you can do with them.
Once you get an idea of the common little issues to look for, you can quickly identify any problems before they cause a bigger problem, and it'll be a great car. Those 3rd gens handle like they're on rails, they're a dream to drive. I've owned 12 RX-7's (one 3rd gen, and around 5 or 6 2nd gens, and the same number of 1st gens)