Well... by now you've probably figured out you got some really bad advice from the LFS
. I really hate all those ads - "... just use a bottle of this and you can add fish in a day!!..." I honestly think these companies do more harm to the hobby than good. But that's a different post, I suppose...
You've got two things going wrong for you right now - the cycle you're going to be getting in to, and the very low salinity.
1. Salinity - You really want to be up around 1.025-1.026, regardless of whether its reef or fish only. The sudden lowering of salinity wasn't terrible - not desirable, but not terrible. Fish seem to tolerate sudden lowering of salinity better than a sudden increase. Quick lowering of salinity is a normal part of hyposalinity treatment for ich, and I've done it several times with no ill effect. As far as the lower salinity and the starfish... I'm thinking it's not going to really tolerate it like the fish will, but there's not much you can do about it. The damage is done. Just keep an eye on it and if it looks like a goner, pull it from the tank before it fouls up the water even more.
You want to slowly increase your SG
up to 1.025, and with critters in there you really don't want to do it more than 0.0005 a day. So if you're at 1.016 now, then tomorrow I'd bump up to 1.0165. You get the idea. If you don't have a refractometer, you're going to need one for this. Besides, you eventually need to get one anyway.
As far as the "how" to increase the SG
, instead of topping off with fresh water, top off with salt water. But on top of that, you're going to have to also change out some of the 1.016 water with a high salinity water. You could make up some salt water at 1.040 and add a little of that for daily water changes - in the right proportions to get you where you want to be.
2. Cycle - With the small amount of live rock and the large amount of fish starting off, sounds like you're going to see a cycle. You're going to see ammonia start to increase, and eventually decrease. Then your nitrites will increase and decrease. Eventually those two things will decrease to zero and your nitrates will increase. At that point, you're cycled. But during the cycle, you're going to want to do water changes to keep the ammonia levels at a somewhat tolerable level for the fish - I'd say 0.25ppm or so. You can't eliminate all the ammonia, since you need it to cycle - but you can at least keep it from spiking too high. The cycle is going to take longer this way, but at least you give your fish a fighting chance.
The other option is if you can get some fully cured live rock - say 50-60 lbs - you could add that and potentially avoid the cycle. (You're probably going to want more rock anyway.) "Fully cured" rock is going to have the bacteria population already living in it, and starting a tank with it often avoids a cycle all together. But it's spendy... expect to pay 8-10$/lb for the stuff. And often times it's questionable if the stuff being sold as "cured" is truly that.
Or the idea Henry had of getting a smaller amount of fully cured rock and starting a smaller tank is an idea.
The salinity and the cycle issues aren't impossible problems to deal with. It's just a rough start in to the hobby. Read as much stuff as you can on this forum to see how others have dealt with it, and ask questions, and you'll get through it.