How much can I make hauling fuel locally with own truck?

Yes, it can be a good thing but bear in mind it's gonna depend on how much business you do. You need to be able to do at least 5 loads a day. In my neck of the woods Austin/San Antonio, it was always best to work at night. That's when the racks weren't as busy. I hauled for a co for 6 years and I enjoyed it til I decided to do something else.
Not sure exactly how much revenue you got per load, but I can check with some friends who are O/O
good luck

 

sounds like a good idea

 

Kind of truck you buy, you can go 2ways. I eventually bought a 06 Pete 387 with a 63" sleeper. But you could just go with a day cab.
Many of the guys went both ways, so it depends on what you want to do. I'm glad I bought a sleeper truck cos the gas hauling co I latched onto were a dead loss. I eventually went and I'm hauling chemicals now for an outfit that also hauls gas in my area. So eventually I may drift back into gas. It's a good business.
on income wise, I recall a buddy of mine claimed he was grossing $20k mth in Corpus Christi TX but I'm sure you should be bringing in $15-20K mth gross so you will have to figure out what your nett will be. But it all comes down to load volume.
But I have a feeling every area is different. Be good just to ask around and see if any of the guys will give you the skinny on gross income. Texas could be a different ball game to Wisconsin for instance. But it really is a fun business to be in.
Good luck