Definitely try to get more rock in your tank. When I started out I didn't really have enough LR but because of the price I thought I could get by without it. I had all sorts of problems with algae and such. After getting more rock, the algae wasn't so bad but it still had a foothold and I wished I had bought more rock earlier. I would definitely try to get more rock in there before you increase your bioload.
The addition of more rock will also allow you to ditch the mechanical filtration (only if you want to). The mechanical filter is something that you really have to watch and clean fairly often as lots of detritus can build up and any sponges inside can become nitrate factories for bacteria.
It sounds like you have a pretty good setup though
