I dont really do anything special re the clams, clams need good lighting and low flow.
If you have zero nitrate then you should be adding ammonia to get the nitrates up a little as they dont like zero nitrates.
Good to have clams on a rock as they will attached themselves.
Not yet, he is in my sump. i have mainly acropora in my sump which he does not touch.
They can nip on corals like brains, xenia etc. al depends on the fish as some will nip and some wont.
Might try to auction some off oneday, hard coral to get.
Collected mine over the last 6 years.
Might try to frag some when i get time.