The Raspberry Pi Thread

I am running PiHole, Plex, Samba, and Deluge Seedbox on my Rpi 4, 4GB version. I have an RPi 3 B+ lying spare. What else can I deploy on my home network that would make it a better and more secure environment? I was thinking of a VPN server, a mail server (for my own domain), and a DNS server. Please share your views on running these servers on RPi, and if you have some ideas or alternatives for the same or different to add.
You can run n8n on your RPI4. It can do some simple automations. Also hosting your own mail is not recommended but for learning you can try it.
 
I am running PiHole, Plex, Samba, and Deluge Seedbox on my Rpi 4, 4GB version. I have an RPi 3 B+ lying spare. What else can I deploy on my home network that would make it a better and more secure environment? I was thinking of a VPN server, a mail server (for my own domain), and a DNS server. Please share your views on running these servers on RPi, and if you have some ideas or alternatives for the same or different to add.
How does it fare? Can it handle 4K video transcoding? And, in your experience, will everything else work fine when doing that? I especially don't want to affect my network latency, so I keep my Pi pretty light
 
4K content I avoid like the plague because even on 1080P, the H.265 profile content lags quite a lot in Plex, which is visible in the form of frequent buffering over home WiFi. VLC plays 99% of 1080P content without any issue. To date, I'm not able to identify where the bottleneck is, bandwidth or processing power? If splitting the load would help, then I would rather shift NAS and Seedbox duties to RPi 3 B+ and keep PMS and PiHole on RPi 4