ViaAqua 100-Watt Quartz Glass Submersible Heater with Built-in Thermostat

Works great fully submerged horizontally. My concern is when I went to move it, it burnt me. Anyone had trouble with snails or fish getting burned? Is this normal for heaters?

can i set a temperature to a certain degree ( that I want my tank to be ) and will it maintain for me ? or do i have to keep turning it on and off?

Which size should I get for my tank? It's a 10 gallon tank. the 50 watt or the 100 watt?

Can this heat up to low 90's degrees?