You will have room for other things in the tank when the anemone is small. However, if you plan on keeping only this tank for the next 5+ years, and feed heavily, your BTA could end up nearly 20" across. Even still, with good planning, you should be able to keep the ned and other corals happy for some time.
Is this your first SW tank? First attempt at a nem?
The reason I ask, is because it seems like it's a first for both, and in that case I'd recommend you be patient and wait until at least the end of Feb. before getting your nem in there. Earlier would technically be possible, but without experience you might not catch the subtle signs of deteriorating health until it's too late, and we (and you) wouldn't want that.
Setup otherwise looks good. What temp color are your bulbs? brand and color? IMO actinic T5 bulbs aren't very useful. You can get nearly identical colors from the AquaBlue Plus, but they pack considerably more PAR. The KZ Fiji Purple is my favorite bulb (though I think ATI might also make a purple bulb now too?). It really makes the reds POP - so think about that if you end up with an RBTA.
Are you going to be running a sump? If so, you wouldn't necessarily need a protein skimmer if your bioload is on the lighter side and you perform routine water changes. In that case, load up your sump with Cheato to help remove nutrients. A skimmer is definitely recommended though - helps keep everything in check between water changes.
Good luck! Glad to see you researching diligently in advance - you'll soon be an expert!