]1) "Mr Bingley might like you the best of the party"

]Is Mr Bennet completely making fun of Mrs Bennet and any vanity she might have left over from former days, or does he still find her beautiful? Is this a completely hard comment or is he showing a brief bit of sentimentality? I can't make up my mind.

I think Mr Bennet is making fun of Mrs Bennet. I don't mean to say that Mrs Bennet is not pretty, very likely she is. I just don't think Mr Bennet meant what he said by his exact words at the time. (Usually what he says is not exactly what he means.)

]2) Really, should Mr Bennet have stood up to Mrs Bennet in the matter of the horse for Jane? Usually, he seems to give his wife her own way so as to preserve peace in the family, but in this instance, I feel it would have been the right thing, both as a father and as a gentleman, to realize what a potentially embarrassing situation this would put Jane in and to stand up for her.

Yes, he should have. IMO he know what is proper and what is improper.