I would reccomend smaller pieces of food for the LTA. If its too large it wont be able to digest it, and will spit it back up.....partially digested. And then you'll have to fish it out before it fouls your tank.
Assuming you have a Macrodactyla doreensis (Long-tentacle or corkscrew anemone), I would feed it bits of silversides or lancefish. They can be picky on crustacean meat, but will accept table shrimp. Thaw out a silverside, and cut it to smaller pieces. Feed one piece at a time to see the anemone's reaction.
Overfeeding your anemone will not happen, since the anemone will just regurgitate it out. However, it does pollute your tank much more quickly as it is more nutrients and proteins to take out.
As for the clownfish, assuming you have Amphiprion frenatus (Tomato clown), they are along the more vicious clown species. If you have one Tomato clown only, I would not get the Amphiprion ocellaris or Amphiprion percula. This is because the Tomato clown will eventually (if its not already) become a female, and as she ages you will notice the body become darker brown beginning from the back of the eye to the tail. The clown's face and fins will be either orange or red. Female tomato clowns are usually vicious to human hands hehe, much like Clarkii's. However, they are a bit tamer to other fish in the tank.
If you have a pair of Tomato clowns, and think about getting a pair of Ocellaris or Percula clowns, it is doable. I recommend getting a separate anemone for both pairs. Possibly a Bubble tip anemone for the Tomato's and later down the road maybe a Heteractis crispa (Sebae anemone) or a Carpet Haddoni anemone for the pair of clowns.
Anemones need stable tank water and good lighting, and as clowns do not need anemones to survive in our tanks, I would think first before getting those other anemones