@Vezelay I think your dress is lovely. Its such a nice fresh fabric. I know you say its out of your comfort zone but I think it looks fab.
I think you could go a tad shorter in the hem length but before you commit I would try sitting down in the dress to check you are not showing too much leg (unless you want to, of course
)
The neckline looks fine to me.
As for the arms you are right to think its still only March but most of the wedding venues in York are well heated but some of the churches are not so cosy!
I bet you get so many compliments you decide to keep it as a dress. We all need one smart dress in our lives.