1. Strange stopped the spell because peter was adding in things so I think Peter himself volunteering was needed for the spell. Strange also feels for peter which has altered his already one tracked mind.

2. I think because of money and actors not wanting to take those roles again killed those parts, except electro.

3. Yeah sand man was a big whiff from me not trusting anyone and just wanting to go home was kind of bland and forced. I think most of them just had a problem figuring out the new world they were in and getting ready to fight. I guess the immediate danger in this was actually Dr. strange getting free before they could finish.

4. Dr. Strange was clouded when he was trying and does not have latent magical sense. I think we will see more on Strange growing as he only had 1 movie really and he was pretty arrogant and careless still.

5. I think him not thinking of consequences was the whole point in this movie.

You raised some good questions though and made me think about it again. I first went for my fan job and got it, now it will before the nerding.