Going to put it straight out there... If all the business requirements are minimum cost and minimum features, Meraki isn't for you.
You can easily get cheaper firewalls with less features (heck, even running opensense on a raspberry pi would do that job), but will have tradeoffs in other areas.
With that said, if you're looking for a security appliance which is easy to use and manage and provides some decent base features, and are willing to pay a little more, Meraki is a good fit.
To answer your questions:
1. Yes, a Meraki MX security appliance is compatible with other vendor switches (including Cisco small business).
2. If you don't renew your license subscription on your Meraki devices, you have a 30 day grace period before your devices stop functioning completely.