Can I use 3 jalapenos in place of 1 habanero?
Yes, you can usually make that substitution without a problem. The key thing in substituting peppers is that you like the substitution. So, experimentation is necessary to find what is ideal for you.

Personally, I like the flavor (separate from the heat) of habanero peppers more than I like the flavor of jalapenos, but I usually have jalapenos on hand. So I often make that substitution and then just add crushed red pepper flakes or cayenne to make up the difference in heat because I'm a big-time chili-head. Doing it that way, you don't need to use more jalapenos than you would habaneros, but you can. After all, it's your dish.