Dude, even though it certainly can be done, the last thing you wanna do is burn down your house or have sleepless nights worrying if you wired it right and the possible problems from that.
I had two tents fully setup in my garage (all the fixin's, so they were kind of a bitch), then realized that the 40 amps I thought I had was really only 20.
Long story short, broke it all down, put it in my workout room, and called an electrician to give me another 40 amps to the garage.
Took him a couple of hours and ran me about $400 all-in - however, the peace of mind from knowing that my house isn't going to burn down is priceless.
I DIY anything I can (mainly because I like knowing how my shit works), but electric is something I leave for the pros - hell, I know more than you about it (based on your posts in this thread) and I still won't fuck with it.
Hire a pro - for the cost of a light you can sleep well at night.
EDIT: and no matter how old or shitty the wiring on your house, I'm beyond positive you don't need to worry about overloading your main feed unless you have a computer server room in your basement or you live in a Smurf hut.
You're drawing like 20-30 amps max, and even old houses (assuming US) have 100 amp service.
You might need to try and run your dishwasher and/or washing machine/dryer when the flowering room is "off", but other than that you'll be fine.
