starfish is not going to help much. In fact, you'd be lucky to keep any starfish alive for a reasonable amount of time in a tank that size. It just won't produce enough of the right foods for it. And the algae building on the glass usually is not eaten by most starfish you see. fwiw, most starfish are not reef safe and do eat corals, and the few that are, are not always the easiest citters to keep alive. And please, do not go buy a sandsifting starfish for that tank. If you go to a LFS and ask about starfish, they are most likely going to try and sell ya one. Not a good addition for most reeftanks, especially one that size. it'll be dead within a year.
Turbo snails are kinda big, and in a 20g nano (i have one too, so I know what I'm talking about with this one) they will be knocking crap over all the time. I would highly recommend you get some smaller snails, and a variety of them at that. Don't stick with just one type of snail. Different snails eat on different foods. Detirtus, algae, diatoms, ect. ect. ect. Also, different snails tend to hit up different area's of a tank. Some like the glass, others the sandbed, others the rock, ect ect.
FWIW, you're tank is a month old?, that's fairly new and will have algae for awhile. It takes time for a tank to mature past that point. You can fight it all you like, but in all likelyhood until it's a bit more mature, you'll have algae showing up. Give the tank 3-4 months before you try to "battle" the algae heavily. A typical clean up crew should be able to handle the tank just fine.