Chlorines can also act as pi-donors, although they are much poorer pi-donors than nitrogen or oxygen.

I would say that pi-donation makes cationic polymerization a much more likely reaction pathway for vinyl ethers, although radical polymerization is not unprecedented. See here: https://pubs.acs.org/doi/10.1021/acs.macromol.6b00145

You are right. Fixed it. Thank you.

That’s an excellent question. There are two ways by which atoms might have partial charge. The first, as you recall, is by examining electronegativities. The second is by analyzing resonance structures, as what we are doing here. It is only by analyzing the resonance structures (and the second-best resonance form, D) that helps us understand why there is a partial negative charge on the carbon.

Fixed. Thanks for catching that!