Regarding your points:

]This is Anne's point of view and not necessarily accurate.
I agree. In my original statement I said that it was Anne's conclusion, but didn't state outright that she could be wrong.

]It might be more accurate to say that he is not yet in love..
I also agree with you on this. There is nothing in the text to suggest that he would not fall in love.

]What exactly should he have done on the walk home from Winthrop?
This is the crux of the matter. We are told:

Every thing now marked out Louisa for Captain Wentworth: nothing could be plainer; and where many divisions were necessary, or even where they were not, they walked side by side nearly as much as the other two. In a long strip of meadow land, where there was ample space for all, they were thus divided, forming three distinct parties; Chapter 10

This was, indeed, the first time that Louisa was singled out by Captain Wentworth and it appears that he was happy to take advantage of the situation by attending to Louisa. There were opportunities for Captain Wentworth to give attention to others where the "many divisions" were not necessary. Though it might not have been easy to give attention to the others because of the way the parties were separated, it would not have been impossible.

Of course, the above quote is also just Anne's interpretation of the situation and she is, IMHO, exceedingly sensitive about the Captain's behaviour.