So, I'm thinking about going Turbo... Questions

[cali yaris]

might have a deal coming up soon on a Blitz

and yeah, anything more than that is a serious project. Even getting the Blitz installed right is tedious and of at least medium difficulty.

How important is tuning going to be if I'm able to keep almost everything stock, and simply add a piggyback system if necessary?

This tells me right there that you didn't search this forum and read a bunch before posting. May I suggest you do that now? Your subsequent questions will be more focused, and more informed.