You really need to give us a few examples of your use of "all get out" in sentences. Otherwise, it's hard to know if you're using it correctly. However, it seems you generally understand the idea of the English phrase.I don't speak Italian but do know French and can deduce the meaning of "tantissimo". Yes, the idea is similar: "to the utmost degree" or, more colloquially, "to the max" (to the maximum). We use "all get out" with like /as: It was as cold as all get out. (It was extremely cold).