If I or someone I personally know were just starting out on a limited budget and were still learning how to light, I guess my advice would be this:
Just get yourself a
Cowboy Studio Kit for under $500 and you're well on your way with most everything you could need to get started, from lights and stands to modifiers and triggers. It's about the biggest bang for the buck you can find.
Yes, there's a good chance you'll eventually outgrow it and want much better studio gear later if you stick with studio portraiture, but the great gear you may eventually want costs serious money, and you can replace or supplement it piece by piece if you find that you're actually being limited by anything in your starter kit, if and when that actually happens. That might not be for years, or it might not be ever, depending on your needs and your style as it develops.
As for backdrops, you need a white, a black, and maybe a gray. With those and
a pack of full size gels, some
gaffers tape (which has about a million uses around the studio) or a
gel holder or two, you can have any/every color under the sun for your backdrop, at will - you can even get creative and do multi-colors. With some creative use of objects between them and the lights, you can have have any number of patterns on them as well. Try all kinds of stuff, like glasses of water, especially glasses or other containers that have irregular shapped glass, plants, lacey cloth or netting, bubble wrap, irregular ripped strips of toilet paper hung between your light source and your backdrop, etc. The possibilities are endless. You can even use your plain backgrounds to drop in digital backgrounds later in photoshop, and those digital backgrounds are cheap too.
You didn't mention a tripod, but if you don't have one, get one.
Also, you'll want/need a couple of
5 in 1 reflector/diffuser/flag kits, and I recommend the stands and arms to hold them if you don't want to be fumbling about with trying to position them and keep them in place. Snoots can be made from cardboard boxes yourself with minimal time and effort. Cover them in black gaffers tape to look professional to your clients. Grids can come in handy too, and can be made as a DIY project out of coroplast, but you can find them fairly inexpensively these days, so it's hardly worth the time to DIY them yourself anymore.
As for books, "Understanding Exposure", "Light, Science and Magic" and "The Photographers Eye" are standards. Beyond that, I recommend Joe McNally's "Hot Shoe Diaries" and "The Moment It Clicks" for some great ideas on how to use lights in very easy but creative ways, especially for photographing people. A good, down-to-Earth resource on the net for learning to light from the very most basic starting place on up to more advanced methods is
The Strobist Blog, and you can't beat the price - it's free. Start at
Lighting 101 and go from there.
The lenses you have now are just fine for starting out. Don't be bamboozled by trash talk about kit lenses. They may not be the top of the line, but they're not junk either. With proper composition so that you have little or no cropping before printing, and care when focusing and shooting to avoid camera shake blur, they'll produce images that are just fine. Use them, use them well, and don't worry about getting better lenses until the ones you have actually limit you in some way. Later on, if you actually stick with this and find a NEED for better lenses, you can spend a thousand dollars plus on a professional quality portrait lens that will shoot at f/1.2, then stop it down to f/4.5-f/8 anyway so that your subjects' ears and noses will be in focus, along with their eyes. By that time, you'll probably be looking for a full-frame camera as well, so start saving your pennies.