My advice is: drink 5 litters of pure water a day
Not. There is no evidence that drinking excess amounts of water helps to combat AMS. It is even possible to get sick, with symptoms mimicking AMS, by drinking too much. Adjusting to high altitude causes more urine output which should be compensated within reason, that much is true, but water is not medication against AMS. Drink only as much as needed to keep the balance, and that includes tea, soup, beer etc.
About the camera issue: If you are going to Dolpo, you are going to have porters, as it is a restricted area without tourism infrastructure. That means having a guide and a camping crew. Hiring a personal porter to walk with you and carry camera gear would cost about $15/day extra. That is not much considering the total expense and well worth it if you want to take heavier kit.
I have walked AC with Canon D5 + 24-105mm zoom, and Annapurna Sanctuary trek with Nikon D800e + 24-120mm lens. Not too heavy to carry in the day pack, as I always have used porters to carry the main luggage. In the eighties I had 2 Olympus bodies and 21, 50 & 135mm lenses and a Widelux F7 panoramic camera for 7 months hanging on my hip 24/7 in a small camera bag in SAE, China, Tibet and Nepal. Not to mention hundreds of roll of KodaChrome. Anyway, spare camera (P&S?) is of course needed if the main one fails. During the Annapurna BC trek last year some condensation formed inside the 24-120mm Nikkor, as it was pouring for over a week. Dolpo & Annapurna should be drier, though, unless your trek during the monsoon.
I also have Fujifilm X-T1 and it is an excellent camera, but I have deep distrust of the batteries it uses, they seem to run out of juice quite fast and quit unexpectedly. In Dolpo you will have to survive without recharging maybe for weeks unless you carry good enough solar chargers or a small generator.
Cold is not a problem for cameras, battery life shortens and cold camera should not be taken straight to warm and moist buildings without being wrapped in a plastic bag while it warms up. Electronics actually like cold.
Wideangles are more useful than long zooms, 135 has really been the longest I have needed, I used to carry a 300mm lens also on my first treks, but quite soon dropped it out.
I have spent almost 7 months trekking in the Nepal Himalaya since -84, so I do have some experience there.