The cleaner shrimp or pistol will not add anything to the bioload and will not be a concern. The only concern is to be sure the other shrimp are larger than the pistol as they can prey on smaller crustaceans at times (rarely).
You could get 2 more chromis but that'd be about it for the fish load. You may also wish to consider a mate for the perc as an althernate. Clowns in general live much longer healthier lives if kept in mated pairs as apposed to solo.
As far as the BTA, you may have to much light once you upgrade to include the additional 2x96w. Contrary to popular belief, BTA's are not intense light anemones. With the amount of LR
you have it should find a decent spot easily enough depending on your aquascaping where it can hide and extend outward as needed. If your water parameters have been stable for several months, you may be fine with the addition. If there has been anything amiss recently I would hold off a few more months. Just be sure you try and get a clone if possible, nothing wild caught.