As a contract security manager… the pi system is better than many off-the-shelf systems. One thing to keep in mind is that you absolutely want to control the data you generate. Every cloud service (ring, etc) will provide free and basically immediate access to your data. This includes if they think YOU are guilty of something. Or if they just tell them you are because their sister/daughter/wife/whatever smiles at you in the park.
If you keep data, they can still subpoena it, and you’d still be obligated to hand it over, but it comes with a lot more paperwork and oversight.
Whatever you go with, software should be open source. Especially if it’s internet connected. This allows third party validation of what is actually happening. Here is a guide on r-pi to create door alarms. You can probably configure something using a pi pico w fire quite a bit less, however, and send it back over a network for reporting. You’d still have to power it, though.
The issue with door alarms is… so you get the alarm, what do you do then? Unless you have some way to review prior video (5-10 minutes, if you get an alarm.) and those cameras show the device in alarm, you have no real way of knowing what’s going on. You’re certainly not going to run home every time.
Most door alarms are false alarms, triggered by people forgetting their code or kids just being kids, etc. calling the cops (or paying a service to call the cops,) is a bad idea.
There’s plenty of guides on pi cams, and those are more useful- you’ll want complete coverage- which means broadly all sides of your house, with close shots on the doors, back gates or shed doors. maybe windows.
One or two cameras are less useful. A hoodie, cap or obstruction can evade that. And in any case cameras are passive systems. They tell you what happened, they don’t stop anything from happening.
The single most effective device is a deadbolt lock on all exterior doors, and bar locks for sliding doors. If your dealing with porch pirates, a chest with padlocks they can then lock (or purpose built chest,) will deter most (but if they really want it, they’ll get it.)