I agree with Scrivens, I believe 10 gallons is only 40 litres?
With fancy goldfish, the recommended stocking I've seen is 20 gallons for the first fish and then 10 gallons for each additional fish thereafter
As for the plant, it looks like elodea densa, a very tasty plant for goldfish
I wouldn't worry too much about her eating it, I have some elodea that my goldfish loves to munch on.
I wouldn't worry too much about the algae either, you can just clean it off the glass with an old credit card or something similar.
In my goldfish's tank I left an entire side for the algae to grow on and she loves to graze on it.
As for the snails, I am not sure what breed they are? Pinkish coloured? Could they be Pink Ramshorn snails?