I bought my first dslr, an Olympus, about 18 months ago and from that experience I'll share a couple things I learned on the way.
1. I wouldn't recommend buying a "starter" camera if you "willing" to buy a different one later. I did that thinking I would/could afford a better, more expensive camera later and all I accomplished was wasting money on that first dslr when I upgraded.
2. There are a lot of different brands on the market, so do your homework. Best case scenario is you're able to find someone who will allow you to "demo" theirs. I was lucky enough to work with a fellow who had a Canon 40D which he let me use (after I already bought the Olympus) for a few days. I was very happy with the results and what I learned along the way.
3. Don't get so caught up in megapixels, personally I would sacrifice mp to save a few hundred dollars if possible. But maybe that's just me.
4. Buy from a reputable retailer. I've had nothing but great success in my dealings with Adorama, my friend from work likes Beach and I've nothing but good things about B&H. IF A DEAL SOUNDS TOO GOOD TO BE TRUE, IT IS!
5. Don't be afraid to buy used, at least if you're buying it from a reputable retailer. Or try eBay, I got a fantastic deal on a Tamron 28-300 there last month.
6. Changing lens is a pain in the butt. Of course you'll be changing lenses at some point, but I thought it was a pain when I had to stop what I was doing and switch out lenses in order to get the shot. My "walkaround" lens is a 28-300, which gives me a very nice range in which to work.
7. Do your homework. There's a reason a Nikon and Canon are the most popular brands!
8. Ultimately it's up to you, it's what you like, makes you happy and gives you the best results.
I hope this helps. Have fun!