Quite a few questions here, I've answered the below.
What's the max number of cameras you can connect?
On my setup, I can have a maximum of 4 but that's just limited by the available ports on my switch.
What PoE switch are you using?
D-Link 1008P
How much disk space does it utalise recording at 2048x1536 resolution at 20fps over a 7 day loop period?
I've allocated each camera 500GB on my 6TB NAS (4x3TB Raid 6), the other 5TB is used as normal storage for my videos, music, documents etc. I've got the cameras set to record at 12Mbps, as I'm only recording when motion is detected I'm using about 20GB of storage a day per camera. Once the storage is full the camera automatically deletes old recordings.
The same for 1920X1080p 30fps?
You can set the bit rate yourself, anything from 4Mbps-16Mbps regardless of frame size and frame rate.
What recording software are you using?
I'm just using the software built into each camera for recording and scheduling, there is client software available and also a mobile app, which you can use to playback full res recordings or watch the low bit rate stream or full res stream live.
What was the total cost if you don't mind me asking?
The cameras were £160 each, switch was £60 and the Microserver and disks came to £500 but I didn't buy the server and disks solely for this.
What's the build quality like on those cameras?
Excellent build quality, they are metal bodied and feel pretty solid.
Also what compression / quality settings etc?
Bit rate on the main stream can be set from 4Mbps to 16Mbps, you can change the frame size from 1920x1080 to 2068x1560 and the frame rate goes from 1fps to 30fps (max 20fps at 2068x1560). There's loads of other settings for adjusting gain, sharpness, brightness, IR on/off, noise reduction, bw/colour etc..
Motion detection / record
Video Blind and alarm (or email etc)
Video Loss and alarm (or email etc)
Disk errors / full etc...
You can set email alerts for any of the above.
Also does it allow you to search by camera / type of recording and then highlight in red (on a time line) all the motion detection....
the limitation with the built in software is that you can only schedule one type of recording so if I had it on 24/7 recording I couldn't set a separate trigger for motion detection that would mark a warning on the viewer timeline, however the trigger does appear in the log so you can use that for reference. As I've got mine in motion detection only mode that doesn't matter to me, the motion detection is very good to and you can adjust the sensitivity, I found at night I had the sensitivity too high as it was being set off by the video noise.
Any other questions let me know!