2. KeepassXC has a browser extension.
3. Refer to point 1.
4. Using a keyfile is optional and IMO don't see how it adds any security benefits to the master passphrase.
The only reason Bitwarden "just opens" from the last session is because of the very features you have disabled in KeepassXC (remember last used kdbx).
Launching KeepassXC for me has exactly the same steps as Bitwarden has. Open program, put correct passphrase (or insecure PIN on Bitwarden for the lazy folks) and the password database unlocks.