Things you should know? First off, check out
www.m14tfl.com. There is way more M14 knowledge on there than on thehighroad.
Bottom line -- they have a great combination of features that make a rifle great. Sights, trigger, reliability, and accuracy. I have a standard, GI-barreled one and keeping the groups under man-size at 600 yds. is no problem from prone with a sling. Only get good mags... CMI or original GI. Look for a rifle with GI parts... they are higher quality... but if you can't find one, a new one from Springfield Armory is still a great rifle (and has a lifetime warranty). They are a steel receiver and bolt, so you grease them instead of oiling them. There are a lot of different versions of this rifle... mostly in the type of barrel they have. So figure out what kind of barrel you want (weight and length; chrome moly, chrome lined, heavy stainless, etc.). It might help to handle some of them to get a feel for what kind you want. If you're going to scope it, get a quality mount... don't use one of the Springfield mounts. I would recommend an ARMS, Sadlak, or Basset. Or if you want a forward Scout mount, I recommend the Ultimak M8 since it is good quality and is the lowest available.
As for a good, affordable optic: if you go with the scout mount route, lots of people like a co-witnessed red dot sight like an Aimpoint or Aimpoint clone, or a nice scout scope like a Leupold or Burris. Personally I have an ARMS receiver mount, and I just put a Leatherwood CMR 1-4x on it... I haven't been to the range yet with it, but I will let you know. It certainly seems to be a lot of scope for the money. Plenty of people just throw a decent 3-9x scope on them and do just fine. If you get a scope, you want to mount it as low as possible, because you will have to get a cheek rest to get in a proper shooting position... the lower cheek riser you have to use, the better for shooting comfort. And if you can't afford the optics setup right away, don't worry... they have the best iron sights in the world. In fact, if you shoot it a little that way, you might decide you don't even need a scope! Though if you have eye issues I understand.
Anyway, good luck in finding one. In the opinion of me and lots of others, they are still the best battle rifle ever made.