If you buy the TA31F, you wont need the mount, it comes supplied with the scope. If you should happen to need one, you will want the TA51 mount.
Biggest difference between the TA31 series and the TA11 series is the size of the scopes and the eye relief. You wont much notice the half power more with the TA31 or the half power less with the TA11.
TA11 is a noticably larger scope. It offers more generous eye releif than the TA31 series. If a little tight eye relief bothers you, you might consider the TA11.
If shorter eye relief doesnt bother you too much, and really, its not all THAT tight, I would easily recommend the TA31. It has all the same features in a smaller lighter package.
The Chevron reticle of the TA31F you are choosing gives up a little speed over say the donut reticle of the TA31, but it will be a lot easier to be accurate with the chevron reticle out at 300 yards or so.
I think people just have to figure out what sort of shooting they'll be doing most with the gun these optics will be mounted to. If you'll be doing more long range and accurate type shooting, with some fast paced CQB drills, the Chevron is an easy choice. If you will be doing the opposite... a lot of fast paced CQB shooting with some longer range and percision shooting, a reticle like the donut might serve you better.
Good luck! Let us know how you turn out! And we always like PICTURES!