You may want to wait to put the snail in until you have some algae growth so they have something to eat.
Actually, with your live rock you should be fine.
Do you have a quarantine tank set up? If not, get a 10-20 gallon tank, heater, and filter and set it up with the temperature and salinity to match the display tank.. The purpose of this tank is when you get a fish, you quarantine it for 4-6 weeks to make sure it doesn't have a disease and is eating well. If it has a disease you can treat it in the quarantine tank. If you have live rock or invertebrates in your display tank you are very limited as to what you can do to treat diseases, as most medications kill inverts. So, set up a quarantine tank. Believe me, it is worth the money. When I first got my clownfish, I almost lost them to ich (a common marine parasite) while setting up the quarantine tank to treat them. Luckily they survived, but a less hardy fish would almost certainly have died.
Tank looks great! You may want to get a couple more powerheads, it looks like you could use more surface agitation.
Whats the plan for this tank, reef?