]Is it possible Darcy's proposal was spurred on by jealousy of his cousin's attentions to Elizabeth?

It is possible that Mr Darcy is jealous of his cousin. But IMHO, I do not think he proposed becaused of jealousy.

]Also, do you think, if he had been financially independent, Col. Fitzwilliam would have made an offer to Lizzy? He doesn't seem to mind her low connections. Would she have accepted?

Yes, I think he might have made an offer to Lizzy. And Lizzy would not have accepted him unless she was in love with him, and she does not seem to be.