First surveillance system

First off hey all, this is my first post here

I'm tryng to figure out a video surveillance system for a cottage. Cameras would be outdoor and also they would be affected by winter.

I was planning to use 4 to 5 IP cameras, not sure yet. Cameras would be connected with PoE cable to Poe swich and it would be conected to router.

The whole system (router) would be connected to a 4G internet connection. Speed is tested and its giving me around 35Mbit/s download and 30Mbit/s upload.

As far as i know it's possible to have cameras with moving detection. So I was thinking that cameras would upload the content to external server (VPS) which is always available, when motion detectors are on. That would save some disk space.

In worst scenatio all cameras will be uploading video to server. So here is first question, because I'm limited with given upload speed, would I be able to see anything from those videos or should I first save videos locally and after that upload them to server, so I could use a bit bigger bitrate and resolution?

If I will buy for example 1080p camera and I will decide that I should lower resolution or bitrate then are cameras able to take videos with lower quality or do I need to encode the video outside of the camera to get lower quality before sending it to server?

I was also thinking if I could use Raspberry Pi 3 which I already have. There I would run for example zoneminder. Raspberry would stream videos to server and also notify me via XMPP for example if motion detecros detects something. If encoding is needed then I guess that raspberry isn't enough for that and I should buy some NUC for example?

Hopefully you guys could help me a bit

Buy an 4 or 8-ch NVR with PoE inputs. For compatibility reasons, best solution is to get both NVR and cameras from the same producer.

Don't worry about the bandwidth, all NVRs and cameras have at least two streams: main stream (high resolution and bitrate) for recording and sub stream ( lower bitrate and resolution) for LAN/internet live view. If you install NVR (strongly suggested) , all recordings will be done through LAN connection and only remote internet viewing will be done via 4G. Nowadays, internet connections with NVR are usually made by P2P (cloud) connection, so you don't have to forward ports, set DDNS and so on.