Cisco Meraki intro

Hi everybody!
Our robotics team had donated from a local IT company closing up shop 4 ms4320-48fp switches, and a dozen mr18’s. We are trying to set up our space using the equipment and are a tad confused over what features require handing Cisco money for meraki online access. We are using a separate UDM that handles firewall and routing. All we really want the switches to do is handle the in wall ports of the building and the AP’s.
Do we really need the Cisco Meraki subscription? What features would we loose?

Thanks!

The mr18 APs might be flashable to openwrt, depending on hardware version. If they’re the ones I think they are, you should be aware that there’s $20-$30 xiaomi APs on AliExpress that perform better

The mr18’s can easily be flashed with openwrt. What should I do with the switches? Is there a flashing option for them? I feel bad wasting them, but they are not worth it at $400 a year