Kathleen, I think it's great that you want to try this! You've already done some car camping it sounds like, so at least your first foray isn't jumping straight into backpacking. One thing that I've discovered about backpacking is that it really does matter that your pack be COMFORTABLE.
I did a 7-month trip through Europe with a huge, heavy pack and was miserable every time I had to put it on. The fact someone had to hold it while I put it on should have been a clue. When we got back to the States, we ditched our heavy packs and I got a Mountainsmith Bugaboo (or whatever the women's version was called). You're slender, so I'd definitely recommend something that's designed for a woman's narrower shoulders. I ended up not liking the way the Bugaboo packed and it just wasn't very comfortable.
I bought a Gregory Jade 50 2 years ago and I absolutely love it. I've used it on 3 short trips and I feel like I can walk forever. When we've come to a resting point, I've felt like I could stop because I was hungry or thirsty, not because I had to get my pack off my back. I just I posted my gear list on here a few weeks ago and I got some recommendations to switch to a lighter pack, but mine is just so comfortable on me, I can't make that leap yet. My point is, if you go to REI to try packs, make sure they put (Bryce, don't read this) 15-20 pounds in it and walk around the store for 30-45 minutes and see if it starts to be comfortable. (Kathleen, make sure Bryce hasn't fainted at my suggestion of so much weight!) Browse through the clothes again while you're wearing it. (BTW, I just bought some Mountain Hardwear Yuma pants...they are the most comfortable hiking pants I've put on. The waist may be higher than you prefer though. They were pricey at $75 too, much more than I'd normally spend, but they'll last me for years.) For me, I've learned that if my pack is uncomfortable, it really dampens the whole trip, as I spend all my hiking time thinking about how uncomfortable I am and that I can't wait to get my pack off. The last backpacking trip I went on, I think my pack weighed about 17 pounds with food, but without water and I had a great time. We got to the resting point (it was a group trip with Sierra Club) and I took my pack off to lean against, not because I was anxious to get the weight off my shoulders. (I saw tonight there's actually a Gregory Jade 50 in the Gear Swap forum. I have a small, because I'm 5'1".)
Based on suggestions here, I did make the leap to a quilt over a sleeping bag. I've always hated mummy style sleeping bags. I think I tend to toss and turn and the bags get all twisted around me. My quilt arrived today and I'm going to try sleeping under it tonight. I'll also second the opinion someone else made about hammocks. I bought a Warbonnet Blackbird (http://www.warbonnetoutdoors.com/blackbirds.php) last year and I love it. When I took it backpacking, I listened as everyone else talked about sticks and rocks being under them all night and I realized how peacefully I'd slept! It zips up like a cocoon, so no bugs! (I'm with you on the creepy-crawlies...I've camped since I was a kid and I'm definitely not ready for a tarp tent. I want a floor!) Something to consider if you like your first few trips.
Feel free to PM me if you'd like. I enjoyed reading this thread and it's really great to see the women posting! I've been lurking here for awhile now and I always feel like I'm intruding on a guy's club.