I was in a similar situation, bought a house with analog cameras. I ended up replacing all the cameras with modern ones, the analog ones were just soo poor quality it wasnt worth keeping them.
I went with Unifi, which I am happy with, but anything new and IP based should be better than what you have.
which ones? Also looking to make this addition/upgrade soon. Nothing crazy, just being able to see my front & backyard. I already have Unifi AP so it's nice to see that people like the cameras.
Analog security cameras will have terrible resolution, use the existing wire to pull cat5 cables and replace the cameras with moderns high resolution cameras
The DVR is the server. DVRs aren’t really designed to off-load camera feeds and recordings for the sake of security. If you want to build your own server, you’ll need to incorporate analog inputs.
If the issue is viewing the cameras from a mobile device, you can try to get this to work with third party apps. I’ve used an (iOS) app called DMSS to access a DVR similar to what you have.
Also, the benefit of a self contained analog device is, among other things, it doesn’t interfere with your network traffic or rely on your router. Get it a decent battery backup and it can still run when the power’s out. Analog cameras generally look better than IP cameras too.
If you want to up it another level, if your old school DVR supports RTSP, you can probably feed that into something like Frigate for real time alerts and object detection.