I agree with everything rpcrowe said. Yes for DSLR, yes for used, and those were good lens suggestions too.
Keeping in mind the fact that you would be "buying into a system" I would be very careful to pick a "winner" that will continue vigorously producing new bodies and lenses for the next few decades. Canon and Nikon are the 2 biggest players in DSLR, and between them they hold about 85% of market share! Pentax is 3rd, but they have only like 7 or 8% of market share. Old names like Pentax and Olympus really fell behind in the switch from film SLR to digital. They are swinging a little harder now, but if I were starting from scratch like you, I would worry about whether or not a Pentax or Olympus will be able to remain relevant in DSLR's. The Pentax weatherproofing and build are nice (and laudable), and I do hope they give the others a run for their money because competition makes everything better and cheaper. But I'd still worry about the health/vigor of the company if I were thinking of buying into a 4th or 5th place brand. You want them to keep upgrading bodies and lenses apace with the competition, and you also need them to not go belly-up so there will be some resale value for your old stuff when you retire it.