Two observations
1) These are not prepped budwood in that the petioles are still on and would have fallen off on prepped wood.
2) They are in very good shape with swollen buds and should be great.
If your grafts are still green, then you are in good shape. Just keep an eye out for growth below the graft and knock those off, your graft doesn't need the competition.
Regarding my observations above, I like prepped scions, they are easier to wrap and I believe they often push earlier though that is a huge generalization. I have grafted with both and I will jump on scions that look like yours anytime (they look very ready) but I will love it even more "sans petiole."
... and because you asked...
1. What do you think of the quality of the scions based on the attached image? (Very good)
2. Should I assume that I am getting terminal budwood when I order? (No, just scions hopefully with swollen buds)
3. Are cuttings as shown on image generally provided as scions for grafting? (Yes, most certainly yes. Some sellers prepare to order in which case they prep the scion for 10 to 12 days by removing the leafs, and letting the petiole fall off and the buds swell before they harvest and ship to you. This takes time)
4. My scions have been on for three weeks, how much longer before I see growth? (It could be anytime now - 3 to 4 weeks is not unusual, is your tree actively growing?)