You should always fit stays over the type of undergarment you intend to wear the stays with.  A T-shirt and bra, or even a t-shirt alone, will support your bust in a very different way than a shift.  You can see how my Cassandra stays are collapsing slightly at the side, because my bra is lifting my bust inward, leaving a hollow at the sides.  

This isn’t the final sewing-together of panels: this is just a quick assembly so you can do a final fitting before the final assembly of the stays.   You’ll need to either re-sew the seams with stronger stitching if you’re using the Theatrical construction methods, or whip the channels together if you’re using the Historical constructions methods.

Hand sewn eyelets sound fragile.  Will they really withstand strong lacing? Yes, absolutely!  In my experience they are actually stronger and less likely to pull out than metal eyelets.  I’ve never had a hand-sewn eyelet tear out, but I’ve had many metal eyelets tear out.