What sort of sump are you running miracle mud or DSB?
In both cases do not add hermits as they will eat the organisms you are trying to cultivate worms copepods etc.
Snails are good if running a DSB ceriths and nassarus snails are very useful specially in the early days.
If setting up a DSB see if you can get hold of some crud from the bottom of vats used for curing live rock
www.stm-shop.co.uk sell it but you may be able to get a helping hand from your LFS if you explain what you want it for. Also see if you can get some sand from an existing DSB if this is the route you intend to take as it will seed the sand bed.
Just don't add hermits.
Also lighting wise if caulerpa is to be used within the sump it must be lit 24 hours a day this prevents the die back that often occurs with caulerpa you also need to regularly harvest it again so it does not die back.