I'd think a mated pair of clowns would be good next. Friendly ones, like ocellaris or percs - farm raised if you can. They seem more freindly to me. Try mushroom or ricordia too IMO
. I also think adding a brittle star to help that cleanup crew would work also.
Gonna use a QT system for your additions? Got space for a cheap 20g setup? Highly recommended.
The midas blenny is one of my favorites. I'd had one for 4 years or so now. But I'd wait until after you see how the new clowns are doing. Got any ideas on what your final fish population would look like yet?