small fish

Has anyone had any problems with purple lobsters eating their fish? Would the lobster be fine with blennies, gobies, and chromis'? And are they pretty good inverts and easy to care for.....do they have any drawbacks? And how aggressive are they? And are they good in pairs or just one per tank...

Is it possible to put a baby banded cat shark (5") in a 300 gallon reef tank. It will have minimal rock work and a soft sand bed. I am wanting just one and when it gets large I will find a bigger better home for it...if I can even get one. I was worried about it with my clown fish, mandarin...