Forgive me if I'm wrong, but it sounds like you're quite new to the photography business.
While I understand how you might be willing to spend extra bucks for those better equipment on this rare chance of a trip you get, my suggestion would be to be a bit cautious and not go overboard with your equipment.
My reason is not primarily money, but for anyone new to photography I would always recommend to upgrade slowly. Sure, you could spend those extra $2000 for super good Fx camera and perhaps more for very good piece of glass, but you will struggle to use them in the field. Moreover, you would not be able to appreciate the extra bucks you paid for your equipment because you have nothing to compare them with. You will end up paying exorbitant amount of money walking away with mediocre pictures without knowing why.
As I said, my primary concern is not money, it's about learning the value in your equipment. I would suggest buying an entry level camera first. Once you learn the limitations on your camera, then you can make a better informed decision whether this is the route you want to take. If you don't feel like you had that much fun taking pictures as you thought you would, or if those extra weight already a bothersome to you (it only gets heavier from here on out), then it might not be your thing.
But if the end of the day you found your calling, and you have advanced your understanding and technique enough to know that it's only the equipment that's holding you back, then you can consider buying more expensive body and lenses.
Sure, you now have spent money on camera you have to replace, but this way you will learn all the reasons you have to pay more for those more expensive professional cameras.
My general rule of thumb is, let's say you don't know the difference between f/4 and f/2.8 70-200, then it's safe to say you don't need the more expensive ones. Once you use f/4 enough and learn that "geez, only if I have f/2.8, then this particular picture will be a lot better because of these reasons", then you're ready for the upgrade.