Apparently, the BitWarden Server stack requires an x86 processor architecture, which means hosting it on a Pi is not possible. I have searched the web for single-board x86 PCs and found the LattePanda, a good alternative to the Pi. It does have quite the price tag, though.
However, reading up on BitWarden's security mechanisms, their servers actually seem trustworthy. I am no security expert, but what they are saying is:
All data on servers is encrypted using a key derived from your master-password.
Encryption is carried out locally on the user-side so that no transmission with critical data can be intercepted
Your master-password is salted and one-way-hashed before being transmitted to and stored on the server. This process ensures that the master-password cannot be reverse engineered.
In conclusion, even if the server was breached, hackers would only get encrypted data. So, as long as you have a strong master-password, everything should be fine.
I'll have to sleep on this, but I think I am just gonna go the easy route for once. ?