If you can... get rid of the fluval filter... its a disaster in a making... unless you are religious in cleaning that filter like every 5-7 days... and rinse it good.... and lots of water changes
In saltwater systems no mechanical filters are needed.... you rely on your LR and sand and water changes (Once a week and 20%)... seems like you are on a good start on that..you got plenty of LR and sand...
I would instead of using the fluval....add a HOB refugium. They are very popular with Nano systems that are not big enough to require a sump. In the refugium add some sand and cheato and you got a Nitrate Reducing Factory....
Seaclone 100 will be fine for now, but later on depending on your bioload it won't do much.... Remember protein skimmer, lights, and LR are where your budget goes to...
As for your lights... its fine for a FOWLR setup...if you plan on anything with corals...you need to switch your lights....
You will need more water flow as well.... For a tank your size....depending if you want corals or not.... with corals you should be aiming at least 1000-1500 gph total in your tank for soft corals... and even more for SPS corals..
Anyways good start for now...and I am happy to hear you got lots of LR as lots of people cheap out on the rocks...and pay for it later on
