Most of it is off-topic. Same as in Qubes Debian. Qubes-Whonix doesn’t worsen Qubes entropy.
Unspecific to Whonix.
This is the wrong place to ask about Qubes entropy.
I didn’t write that code so I can’t answer that.
Only commenting on /dev/urandom not reviewing full implementation:
Writing to /dev/urandom should be fine.
Quote random(4) — manpages — Debian bookworm — Debian Manpages
Writing to /dev/random or /dev/urandom will update the entropy pool with the data written, […]
Yes I would do this before generating keys.
I don’t have privacy concerns about creating or copying random data into any VM to then feed it into the kernel.