Small Office - VLAN or not to VLAN?

We have a lot of small retail offices throughout the country.

Soon we'll be deploying VOIP at the sites (2 phones).

Right now the networking infrastructure is a single ASA 5506 on a flat network (no vlan)

Devices:

ASA 5506

2-3 computer

1 terminal to take debit/credit payments

1-2 printers

And in the future, possibly IP cameras

Ignoring IP cameras because its not 100% guaranteed. Should I be getting a managed L3 switch like the Cisco SG350 (Any recommendations would be great)... I can't get anything to expensive because of budget constraints.

Or...should I just stick with the ASA 5506...the only concern with this option is some sites have more than 8 devices which eat up all the ports on the 5506...for those sites i'll be forced to slap on an unmanaged switch on to the 5506 for VOIP which will not be good...

Any suggestion/recommendations would be great!