(I didn't see where you may have started a threat on this..)
Suggestions for connectivity between your new pool house and main house:
Simplest would be to go wireless (which I know you do not prefer). If you end up going this route, I would suggest getting a point-to-point wireless bridge. Luxul and other companies make these products. They include a pair of WiFi radios with focused antennas (instead of typical omnidirectional antennas) and outdoor enclosures. Put an Ethernet switch on each end and treat is as a transparent "wire" between the two locations.
If you do trench and pull cable, I'm sure you know the "rule of thumb" to always pull at least two of every cable, every when you think you only need one. If you plan on pulling Ethernet and coax, then at least two of each. Go for the highest rating (cat 6E ?) and highest quality cables. Material cost is a one-time thing but the labor and effort is something you want to last many many years and not have to re-do in the future because of an "oops".
Because a pool house to main house is probably a relatively short run, and is only a single point=to-point connection, I would strongly advise running at least a pair of fiber optic cables also. With only one run, the fiber cost will be reasonable (versus wiring a large port of a house, etc.) and there is so much versatility. Even if you don't use it initially, you have the potential to push anything through a fiber - unlimited video, audio, data, etc. and not have to use any compromise solutions like video-over-IP or HDMI/CEC-over-IP, etc.
For security and IP cameras, books have been written but I would advise considering only cameras that are ONVIF compatible so they can be used with many different front-end apps, applications, or NVR (network video recorder) systems.
FOR NVR, (to keep everything in-house and not pay monthly cloud or hosting fees), the two programs I have used are Blue Iris (for the PC), and Security Spy (for Mac). Both of these are awesome with lots of configuration options and many different ways they can be used. Both of them will give you the "live video multi-camera display in a grid" on your computer that you are looking for.
Last thoughts - SD definition cameras are still cheaper than 720p or 1080p HD cameras. If you are going to use a lot of cameras (4 or 8 or more) consider carefully if you really need all of them to be HD. with SD cameras you will save a lot of money on the cameras, and have less bandwidth (and less storage) to handle their streaming output.
Finally, I would advise paying a little extra to get cameras with H.264 hardware encoding built-in. This will reduce the bandwidth over your LAN and allow the NVR software applications to handle more cameras simultaneously as a lot of the initial video processing is offloaded to the camera itself.