Actually, a build starts with an idea. Then you formulate a plan. Building it all willy-nilly and changing your mind as the wind blows is a waste of money due to missteps, mind changing, etc. Some pro builders can do it on the fly, but they are the exception.
What is the plan? Daily driver? Show bike? Cafe bike? XB clone?
For me, the first course of action is to clean the bike. Ideally, put the bike on a trailer and roll down to your local self serve car wash with a bottle of degreaser and a brush (I used a cheap toilet brush from a dollar store). For degreaser, I like to use Zep heavy duty citrus degreaser, but will also use Zep Fast 505 on really greasy parts (but this can be a little too aggressive).
Secondly, make it run reliably. That way when you get done with the mods, and it wont start/run/idle whatever, you'll know that it did run before you tear it down and what to expect.
Then stop and make a plan. The problem with doing a inexpensive bike like a Blast is that is it easy to go over budget way too easily, and have a bike that is only worth a fraction of what you have into it.