Most modern systems - Honeywell Galaxy, Texecom, Etc. have many zones capability with double balanced circuits. This means that you can detect open and short circuits on each sensor and get a detailed message from the panel to tell you what's going on. You can use existing wiring and sensors. For existing sensors, you just add a couple of resistors to the contacts to make them double balanced. Each active sensor only requires 3 cores and passive sensors 2 cores.
You can also add zone expansion using RIO's (remote I/O) for situations where you have an existing wire going to a point (existing sensor say) and you want to expand to another 8 sensors in that area.
I use the Honeywell Dimension 96 (providing up to 96 detection circuits and 48 outputs) in my own home with two active 115db backlit Texecom sirens, multiple keypads, a power RIO and regular RIO. I have the E080 Ethernet module and SelfMon automation module, so have phone/smart device apps and can control the heating, garage doors, gates and lighting in combination with Home Assistant. The Dimension has a nice big reliable linear power supply - I've never seen one of those go faulty - cannot say the same for Texecom's PSU's which were plagued with issues.
Disclosure - I run the SelfMon self monitoring platform.