This is my opinion on what makes a good photography boat, and my opinion of the effect of the design on the performance, other viewpoints are welcome.
Length – I want a boat that is still efficient but short enough to get around in tight places. For me 16’-16.5’ with some rocker is a good range. You mentioned week long trips and for that I would consider as long as 17.5’ (In fact my next build of the avocet will probably be a 17’ 6” version that is one inch more narrow and 1.5” less height designed for tripping). That gives you a little more storage capacity and more speed without compromising efficiency at typical cruising speed. Top end speed means little in most situations especially photography or tripping I think efficiency is much more important.
Width – I like about 23”-23.5” for photography and paddle 21.5” to 22” for general paddling. For me this gives plenty of stability and still offers some responsiveness. Avocet is 23.2” and 16’ 2” and plenty stable for me. With a 17’ + boat I would drop about ¾ inch of width and maintain similar stability, my 17’6” design is 22.3 inches wide, waterline beam is 20.6”. This may seem counterintuitive but I focus on secondary stability for a few reasons. When I am twisting and photographing I like to be able to feel my lean and have the resistance increase as I lean. If primary stability is overly strong it gives me an awkward stage as I lean into the secondary stability range. I put rudders on all my boats so I can maintain the angle I want as I drift and the subject moves. The more I have photographed the more I like to do a subtle leaned turn instead of the rudder, even at low speeds it can be pretty effective. Again if the primary stability is overly strong it is harder to do a subtle and well controlled lean turn that is not overly aggressive.
Hull Shape – My hull is less flat bottomed than you would think to get the strong secondary stability and relatively lose and tippy primary stability as mentioned above. This also gives me a little less drag. I also have a decent amount of flair on the sides to increase secondary stability and the effect of a leaned turn.
I also like the hull to stay pretty full well into the bow and stern. This improves stability, lessens drag, and gives a very gentle transition when leaning. This will also help with your trip capacity.

I like the height of the cockpit around 10 inches at the back and 13” to 14” in the front so it looks a lot like the old current designs extreme and expedition but the deck is more rounded than peaked. This allows for a lot of mobility in the cockpit and room to work with camera gear. It also increases the freeboard so you are a little less likely to take on a wave. And as with the Avocet it allows for an under the deck, deck bag or hammock which is both good and bad. I go for a pretty long cockpit opening of about 29” again to allow room to work with camera gear and as I get older I do like the easy entry/exit. To keep it from being overly sloppy I use some pretty distinct thigh braces that are easy to disengage from when I need the mobility. I find I put my gear at the most risk during entry and exit so a larger cockpit adds a little value in that area also. This design also allows for massive amounts of water if you do roll and flood. Just a note on underdeck hammocks. They have one big disadvantage for camera gear. I find high humidity for extended time is much worse for electronics than water and if you are paddling with the spray skirt on all the time that is just the environment you are creating. A good dry bag can mitigate the problem to a degree. I am just experimenting with the underdeck bag now and the jury is still out. It clearly catches less wind and looks better than a top side deck bag. Keeps the gear out of the cooking sun and exposes it to a bit less splash as I tend to paddle with the deck bag open most of the time.