[Design] Looking to segregate multiple WAN IP's on a single connection to separate interfaces on firewall. (Access VLANs & Trunk?).

Hi all,

Would appreciate any notes/guidance on something I am planning on implementing.

Backstory: Business is looking to save money by changing ISP. New ISP is able to provide IP space for each sister-business based in the same office but can provide a single router/interface for use.

Plan: I intend on configuring a Cisco (SG Series) switch that will have interfaces 1-3 on separate VLANs (10, 20, 30) and these will be used to connect directly to the firewall on separate physical interfaces. I will then connect the single WAN connection to a trunk port on the Cisco switch and allow for VLANs 10, 20 and 30 to traverse the link.

Example diagram here: https://imgur.com/a/MtubIvt

If anyone reading this has done this before how did it work out for you? Is there anything I should be aware of? It seems fairly straightforward but wanted to get some thoughts on it before proceeding.

Thanks for reading!