You're going to have ask yourself this question: "what kind of pictures do I want to end up with?" From your post you may not need a large DSLR camera, those small "pocket-sized" cameras have incredible zooms now days. We were in Alaska in March to view/shoot the Aurora Boriealis, there was a guy in our tour party that had a Panasonic Lumix with I believe a 20X zoom. While his shots of the Aurora weren't all that great his wildlife shots were! I had my Nikon D90 with the kit lens 55mm to 200mm and his wildlife photos kicked butt on mine! And I had to drag all my (heavy) camera stuff along with me, all he had to do was drop his camera in his shirt pocket. BTW his night-time pictures of the ice sculptures in Fairbanks were great!
There's a lot to be said for large sensor cameras, I wish I had the dough for a full frame camera, my Aurora pictures would've turned out better but what I did get was pretty darn good and besides how often am I going to be in Alaska, in March shooting Northern Lights? Not too often so my DX or APS-C size sensor camera is OK for me.
So it boils down to what you want to spend, how much hassle you can endure lugging around a bunch of photography equipment and how good you want your pictures to turn out, only YOU can answer that question. Do your home work, choose wisely.
Hope this helps.
Dan