I would go with a 3" sandbed otherwise once you get to a year marker in the tank you might get old tank syndrome where your nitrate spikes and wont go down the DSB
will help alleviate most of that headache. Make sure the way you have your rock set up and aquascaped that water can freely circulate in, through and around it other wise you'll get dead spots that will cause nitrate spikes in the future. For sure switch to 2 power heads opposed to one. 2 425's should be fine and koralia has its own wavemaker now that you can pick up for about $80. Are you running carbon, GFO
, or chemipure? And you might want to get a HOB
skimmer like a eshopps PSK-75. Great cheap skimmer. Have one on my 12g nano. and have their bigger PSK-100 on my 55g. Run with the damsels 1-3 might be best. feed everyday and the tank should cycle in a month - 2 months. Its different with each tank. Be patient it will pay off in the end. Once the tank is cycled leave the damsels in there for an additional week then take them out and replace them with other fish. They are terrorists and very territiorial. If you really like the look of them add them last to the tank so they're at the bottom of the pecking order.
Any thoughts yet of the fish you want in the tank after it cycles? And are your bulbs actinic and at what spectrum?