I could be wrong, but that's how I read it. I let my family know I was growing after I had a few grows under my belt. The alternative to me growing my own marijuana, I explained, would be to continue to buy bags of weed from criminals. This way, I don't fund criminal activity, I don't contribute towards criminal activity because I don't sell any of my yield, ever. I pay my electric bills on time every month, I scrub the air I exhaust from my grow box with a carbon filter so my neighbours don't have to put up with any odours emanating from my apartment. What I'm doing is a victimless crime. I really fail to see what the big deal is with a small, personal grow. Just don't sell it, or boast about what you're doing to all your friends, keep no more than a couple plants at a time, and you should be golden.
You can get small grow tents which are suitable for a few plants, and the good quality ones should be made of non-flammable material. Buy your fittings all wired up for you, and that will safeguard against sketchy electrics catching fire.
Your electric bill will not increase by much per month using a 250w HPS. Check you latest bill summary, and you'll see what they charge you per kilowatt hour. With that information, you'll be able to calculate exactly how much 250 watts running for 18 hours a day (12 hrs during flower) will add to the bill.
I run my lights at night when electricity is cheaper (off-peak). I use 250 watts of CFL, and it doesn't cost me more than $20 a month to run, probably less. My PC uses way more than my grow. So does my beast of a TV.
Get good soil (I'm not a soil grower, I use hydroponics so I can't recommend any), get a pH meter, do most of the stuff you said you didn't do, and you'll be in good shape.
Talk to your mother and make sure she's ok with you starting a safer, more thought-out grow.
EDIT: Marijuana worse than heroin?? Absurd. Statements like that, with respect to your mom, are full of ignorance. No one who knows anything about either product would ever make such a comparison. They are, in fact, incomparable, unless you're the kind of person who can draw comparisons between a shoe and a piece of toast.