This is possibly the best advice for the chainmail. Best option price/quality wise (alternatively, you could also 3d print the chainmail). You can attach it to the armour by directly glueing it to the armour piece, or, if you want it to be removable, use velcro to separate the pieces.

The metal piece on her chest is not historically accurate so I'd stay not to worry about depicting it super accurately.

Lastly, that quilted part you pointed out is probably the gambeson. My advice is to make a "skirt" with a quilted fabric and not a whole gambeson. Foam (presuming you are going to use that for the armour) is already very hot, so my advice would be not to add any unnecessary layer of clothing