I took the MSF course about 3 weeks ago to get my motorcycle endorsement on my license, so I can answer any specific questions you have about that process (for Texas anyway).
The MSF course is probably the best investment you can make at this point. As ZV said, if you have never rode a motorcycle before, you'll learn very quickly in the MSF course if you would enjoy it or not. That, and you'll learn critical skills required for riding a vehicle on 2 wheels. Also depending on your state, the MSF course waives the driving portion of the license exam.
Also as ZV said, starting out on a 250cc bike is your best bet. As he mentioned in another thread, a used 250cc bike will hardly depreciate in value (if any), which would be useful if you decide to continue riding and get a bigger bike, or sell it because you don't like riding. As a matter of fact, in the MSF course, we rode 125-250cc motorcycles provided by the instructors.
Expect to spend at least $600 on gear. You don't have to get an expensive helmet to get a good one. I have a Scorpion EXO-700 that's both DOT and Snell certified for $200. I got a textile mesh jacket because of the hot days in Texas, so I didn't spend as much on it ($200). Expect to spend more if you get leather. Same with gloves and pants.
I would advise looking online to get some ideas for gear, then going to a local dealer to try it on. Nothing is worse than having ill-fitting gear (especially the helmet). If you try on a brand in the store and find it cheaper online, then you'll at least know what size that will fit you when you order. I bought all of my gear locally because the prices were comparable to online.
You can bike in a backpack, but because of your sitting position on a sport bike (crotch rocket), you can become easily fatigued starting out if it weighs a lot. Essentially, you will hold yourself up on your bike with your core muscles (abs and back); NOT your arms!!