Questions about new Communication Sites

We have had a 'flat topology' model with different web applications (intranet, team, project, publishing, apps, mysite) since 2012 when we rolled out SP2010. I know many organisations regard their SharePoint environment as 'the intranet', and have placed 'team sites' under a tree structure under the top level 'intranet' site. We made a conscious decision to keep the intranet web application separate from the team/project web apps.

Our on-prem topology consists of 6 web applications, and varying numbers of site collections per web app; 1 for the intranet, around 180 team/project site collections (that use the same template), plus 32 publishing site collections. Team/project sites are limited to one sub-site level. Publishing sites can have more but must relate to the same top level subject matter - we use a lot of publishing sites to publish procedure manuals, for example.

For SPO, where we are restricted to /sites or /teams, all our existing top level team sites will be migrated to /teams. Some sub-sites may end up as Group-based sites because they are more closely aligned to DL structures. Publishing sites will become communication sites. We will continue to maintain a flat topology model.