Is to micro-plane the peel... no white, certainly no lemon juice. Soaking time brings out the oil, and the flavor of the oil.
Sweetness is a matter of taste.... I prefer it less sweet, most like it very sweet... for each batch I will make one that I prefer, less sweet, and one very sweet. But this is a separate process from the process above in which you extract the oil from the lemons.
I used Meyer Lemons.... my favorite. I don't think most people know about Meyer's... which are, for lack of a better way to explain them, somewhat of a cross between a lemon and an orange but leaning more lemon.
Like any sweet liqueur Limoncello you do NOT want to over drink, even though I've never done it my guess is the hangover would kill you.