You can do a simple experiment to find the answer: try walking on the tip of feet. It is possible to walk that way, and with slightly stronger fingers and pads under them it would not hurt, but the balance would be really awful. I think longer/larger feet are necessary for balance...
I have nothing to add to this. I'm not so good at dog anatomy, but it looks almost perfect.
I've looked at your bone chart on your site: I suggest you to use a human-like pelvis, because I think it's the best solution for a prolonged bipedal stance. Apes and birds can have a bipedal stance, but birds have a very peculiar structure fit for landing, and apes can't stay on their feet too long because, if I recall correctly, their glutei aren't enough developed for it (or something like this, I can't remember correctly ).
As usual, you did an awesome work.
The pelvis will be quite human-like, there is just an extra part on the back, under the glutei. I'm gonna draw it better later. I think you may be right about apes, the glutei are exceptionally large in humans compared with other animals and they keep the legs straight. The glutei here are developed as much as human ones.