Inherited system with no docs- help?

We just closed on a house, and as part of it we were left a SimpliSafe system, installed and ready to go. The only trouble is that no manuals or information were left with it, so we have no idea how to set it up, configure it for our family, engage monitoring services, etc. I am hoping you can help.

There are no identifying marks on anything indicating what model or how old it is except for a serial number on the bottom of the base: #1F218E. I am hoping between that and maybe some pictures of the unit (which looks a little different than the one in your ads I think) and keypad you can help me get started with some guidance and documentation. There is no QR code on the bottom as newer models seem to have, the base looks a little more slender than the current pictures I've seen, and the keypad is an LCD screen.

Photos:
https://photos.app.goo.gl/8p3yAYY1pMNRaKKYA

One question I have: if it turns out this unit is hopelessly outdated, can we upgrade the base unit and keypad without upgrading all of the sensors in the house (there are a lot!)?

Thank you in advance for any help you can render!

Matt