I didn't doubt that he was rich, but I thought he was likely an abusive jerk like Will's father. I wondered if Will's instant dislike of the man was more about his mother possibly ending up with Awful Husband 2.0 , especially when she didn't have to. It seems that she was left with enough money to live comfortably, if not at the same level as before. As far as he was concerned, she was free.
As far as Ellie goes, I don't have a problem with her turning down his proposal. Sure, it was a little harsh, but I can see her being taken aback. They had only been on one actual date! And of course, there's the bigger issue of whether you should ever consider being a vicar's wife if you clearly feel a certain way about religion, which apparently she had made clear to Will already. So, no, Ellie was clearly not ready to say yes to a proposal right now.
That said, I actually like them as a potential couple.And I'm glad that Will has gotten over the rejection and that they've agreed to start over as friends getting to know each other properly.