I have peppermints, blue legs, snails...none of them bother my fish or corals at all. Dont know about the emerald and lightfoot, but I donthtink they will hurt anyhting. In my 120, I have 5 peppermints...love those guys, about 125 snails, and 50 crabs. I dont reallythink I could accomodate any more.
Two things you may want to consider...
1. If these snails are like the nassarius, mine live under the sand all day and come up during feeding or for a little cruise at night. Will you have enough sand space for 350 under your sand? They are small, but I know when I add new ones, they like space and move away from each other. They dont want to be near one another unless its mating time. Yikes! Wait until mating time. My kids said Mom, why are all the snails on side of the tank? I told them they were having a party! Mine have got to be the horniest snails alive. Eggs everywhere!!! I would hate to see the mess 350 would make! I dont htink I would want more than 80 in my 120 gal. tank.
2. Also, I'm not sure these guys do your rock and glass? I would be concerned about having so many of one breed. I have lke 80 nassarius, 20 turbos, and 25 ceriths, all with different cleaning assignments. Personally, I think it would be better to have different types in there to make sure all jobs are getting done.
Maybe Bill will trade you some of these for some other varieties??? Also, MJ might buy a handful from you. She could use a few more.
Good luck.