Great start! So, I do ride with kevlar pants (with armored shorts and strap on knee armor) sometimes, but here's what I've decided: if you're gonna go that route, you need to get TONS of kevlar. Funny enough, one of the best-rated pairs of kevlar riding pants are from the Competition Accessories house brand, Sliders. And bonus, they're usually even a little cheaper than those Joe Rocket pants. But they have huge, connected sections of Kevlar inside them, and were rated by one of the big moto-mags as one of the best kevlar pants you can buy (right up there with Draggin Jeans, which are twice as much).
For reference, under my kevlar gear, I wear: Dianese Hard Armor Shorts and Knox Cross Long strap-on knee armor.
Keep being smart!
NinjaEDIT: Oh, and about back protection. I started out upgrading the back armor in all of my jackets, but then I realized that I was spending $40-50 bucks upgrade on every new jacket, and the inserts were usually shaped specifically for that jacket, and so couldn't be used with others. I finally bit the bullet and bought a separate back-protector (actually back and chest armor 'track vest' to go under the jacket). This is what I would recommend doing from the beginning, if you're serious about protection. The armor is better than any insert, it stays put better, and you can use it with every jacket or suit you ever buy. I went with A* because of a clearance event, but KNOX, Forcefield and several others make great quality back protectors.