Woah, hold on there. Why do you want the Tactical Entry model? The R4 (M4) barrel is the ass-backwards barrel designed for a grenade launcher and the elevated rail/carry handle thing is pretty much useless for a lot of people. My advice, get a CAR-A4 instead and a nice rear sight. It will give you more options, lines the optic up better if you're using a mount, and it's cheaper.
Also, hold off on the optics for a while and learn how to shoot with your irons FIRST. Once you can hit something with irons and have an idea of what you want in a scope from actual shooting experience, then start looking for one. You never know, you might find out all the shooting you'll be doing will be under 100 yards, in which case an Aimpoint or EOTech would do the trick. Or, you might like shooting something really far out, in which case a normal scope would be better. So, get a nice RRA with a good set of rear irons, put about 1000 rounds through it, then start looking for a scope. You'll thank yourself later that you did.