I think it's ok to argue with your fiancee on a few matters, BUT when it comes to wedding details..give her your utmost support because whether you like it or not it is the bride who ultimately makes the decisions with this things. .well at least that's what happened with my wedding.
When it comes to online purchases, I always follow up via email or call the hotline - feel free to nag them if you want to there's no harm in following up plus that's what their customer service is for.
There are so many options for online made to measure suits or shirts, but if you're ordering online you have to be sure of your measurements as some online MTMs will ask you for it before proceeding with your order.
Absolutely, it is recommended though when getting fitted to always wear your best fitting clothes so the tailor can make the necessary notes about your style, so there's little room for error on the part of the tailor.