I spent nine nights in Venice last fall, partly to indulge my love of glass. I definitely didn't get to do as much non-glass exploring as I would have liked to, and I am not a serious photographer. I'm confident seven days will not be too long for you.
The one-week vaporetto pass is what you will want. It costs 65 euros, as compared to 9.50 euros for an individual ticket. If you stick with staying on Giudecca, you'll probably be taking at least two vaporetto rides per day, because you have no other (affordable) way to get off that Island. The vaporetto pass will have paid for itself by the fourth day. And then you have a minimum of four trips needed for Murano-Murano-Torcello, even if you cram them into one day. Incidentally, photography was not being allowed inside the Basilica of Santa Maria Assunta on Torcello as of last September.
I spent a couple of hours walking around Giudecca last year. I didn't get all the way to the western end. My impression based on that very limited exposure was that Giudecca is attractive and less tourist-trampled than many other parts of Venice, but perhaps lacking enough architectural variety to keep you from wanting to explore other areas of the city every single day. I wonder whether the need to start many/most of your days with a crack-of-dawn wait for a vaporetto, rather than being able to just leave your lodging and walk a few blocks, will get somewhat frustrating. I'd suggest fiddling around with the vaporetto schedule--or perhaps the chebateo app--to get an idea of the frequency of the boats and time required to reach various destinations for early-morning and late-night photography. I do understand the challenge of finding an affordable place to stay for such a long visit to Venice; I was fortunate (and grateful) to have someone splitting the lodging cost with me.
If you're interested in indoor photography, the very inexpensive Chorus Pass will be worthwhile. It covers at least a dozen of the less famous churches. Even though you probably won't end up going to all of them, you should find yourself near enough of them to at least break even. It's nice not to have to keep fumbling for 3 euros, or whatever the individual entry fee is.
You can buy both the Chorus Pass and the vaporetto pass at the tourist office in the train station. I don't think the more costly city sightseeing pass would fit your plans. As a photographer, you're going to want to wander down any calle that beckons, not design a sightseeing schedule that smashes a bunch of high-traffic sights into as short a pass period as possible.
