Congrats on the Brompton acquisition! Some Q’s have already answered by others, so here’s mine:

4. - You can get the Brompton Carrier Block and a Brompton Carrying Frame without a bag to attach your own bag to. If the frame is too wide and you want to customize it to your bag, you can simply drill out the rivets that hold the metal frame, cut them to the desired length, then rivet it all back together.

I also have the newly designed Brompton Basket, and it's very good for a basic open basket that can be cinched closed. It easily holds a big backpack when I need that, and I also carry a raincover for it since it's open on top.