I really like the close-up lens idea, will definitely pack one of those.
The DA200 is 245 gram lighter than the 300 but at 825 grams, the 200 is already on the heavy side, so I think I'd still rather take the 300 and the TC, for the overall greater reach. The good news is that I've managed to convince the girlfriend to carry the DA300
I have to confess, tempted by my own research, I checked out the D3500 with its 18-55 kit lens and that kit is about as heavy as three Kit Kat bars.. yikes.
So, at the moment I am thinking 16-50 always on until it rains then 18-135. In decent weather, 15-31-77 depending on the subject. And the DA300+TC for the birds and such. Like Gary H Perth suggested, I will take this kit out on shorter trips locally and see how my back fares.
Thank you Everyone for your advice, I appreciate it very much.