There isn't any cut and dried process for migrating from an existing RHEL 7.3 server.
You would need to make a list of all of the functions performed by the old server, then figure out how to duplicate each function on your SME server.
I suspect that your old server is managing the multiple web domains by IP address (since you mention eth0, eth0:0, eth0:1, etc) - SME does this using the domain name that is used to request the page - so you can host 10 domains on one server, all sharing port 80 - but browsers are returned the desired website based on the URL that was entered. To do this on a SME server you would:
1) Create an ibay for each website
2) create a "domain" for each virtual domain, and specify which ibay is used to host that domain
3) change your public DNS to return the WAN IP of the SME server for all domains.
More specific help would require a more specific question
