I'll be a small, and very timid, contradictory opinion here. Since it sounds like you've already committed to carrying a minimal amount of light, compact gear, you could buy a modest capacity pack (say, 40 - 50 liters) with a minimal suspension (I'd suggest the Osprey Talon 44 or Kestrel 48, depending on how light a suspension you're comfortable with.) This will help you visualize how much available space you have, and may drive certain other gear selections, such as down v. synthetic sleeping bags or jackets, and may be a deciding factor against buying those "oooh - shiny" things that are easy to justify in the store: you'll decide against that folding aluminum table and chair because, well, they won't fit.

Now, this isn't a recommendation I'd make to most beginners. I only suggest that it might be OK because you seem to already have made some fundamental decisions about what your gear load will look like.

And I'm only about 2/3 sure I really want to make it to you. But, it's out there, for whatever it's worth. Leave out the books and other luxuries, and I'm a bit more comfortable. But, if a big part of what you'll do is haul stuff in so you can entertain yourself in camp, then all bets are off, and I'd agree with everyone else that you need to get everything else first.