Best TM and CCC Setup?

I am trying to setup an easy and efficient Time Machine and Carbon Copy Cloner backup system.

I have the following:

• 2017 iMac 1TB (Wife's primary computer)
• 2017 RMBP 1TB (My primary computer)
• 2015 RMBP 1TB (Secondary/Backup computer)
• 2013 Time Capsule 3TB
• CenturyLink Technicolor C2000T (Wi-Fi) Modem

I assume the 3TB Time Capsule no longer has enough storage for my three Macs so I was thinking of either upgrading the internal HDD, adding an external HDD, or selling it and trying out OS X Server. Any suggestions on an internal HDD and external HDD?

I know many people use a stand alone Mac Mini with DAS for OS X Server but I am not sure how OS X Server effects the functionality of everything else. Instead of purchasing a Mac Mini, could I just add OS X Server and DAS to the iMac or 2015 RMBP?

What would you recommend in my situation?