No.
Yes. You can remove the flash drive after the LUKS partition is unlocked.
Yes, see this guide:
It could boot a little slower since the USB flash drive read speed is lower than SSD but it’s neglectable since it’ll only read somewhere like 200 MiB from the USB flash drive.
But it has a security downside, the same one that described here:
Not sure what do you mean by this.
Can you provide a description of an attack that you have in mind?
Yes, the site seems to be down, it’s not working for me right now as well.
You can read the link in the archive:
https://web.archive.org/web/20240603054254/https://blog.3mdeb.com/2024/2024-04-11-aem_phase4/