I'd suggest trying FairEmail on your phone, https://email.faircode.eu/, before trying to set up an email server.
I would ask if you have good knowledge of IMAP. That allows access to a unified inbox from several devices and you don't have to own the server. It is far preferable to webmail for me.
I host my own email server and use many devices all over IMAP. If you need a server, nixos-mailserver is my recommendation. You could then try Roundcube on top but I bet you will use IMAP instead before you get there.
I am on the path VSCodium --> Lapce under NixOS for visual editors and to decorporate my workflow. i.e. away from VSCode which is [otherwise] exceptional.
If you are limited to signal, its a problem users like https://discuss.tchncs.de/comment/7643631 might not have.
Signal ties you into google or apple and mobile operator so I wonder what its benefits are beyond stopping Facebook monetising peoples data.