Forum Discussion
When to use Team site (classic experience ) which uses modern UI Vs Team sites / Office 365 groups
I would use a comm site for my intranet sites because you get a modern top navigation which looks much better than the left quick launch bar. Eventually in near future we'll get the option to change this on all sites thou but for now comm site is the only way.
Classic vs Team (Group site) is only difference is one is connected to a Office 365 group and the other isn't. With that the site has the Group added to default security (Owner, editor) and can be managed with the group. You can tie Teams / Planner etc. to it. And you get the extra webparts because they are group connector webparts which require a group to be used.
As you discovered you can turn classic site into a group connected site (Groupify) so you can go either method, but the modern way is either using Communication sites for stand alone sites, and then Team site(Group site) for collaboration sites / teams etc.
I use Communication sites for all my org facing intranet sites (Home, HR, IT, Finance etc. ) and they are all joined to a Hub (not subsites) where the Home site is the hub, then join the department sites to that hub, rolling up search and content to all the joined sites. This is the "modern" way of doing subsites.
1) Create an Intranet following the "Flat pattern" structure what means each top site in your Intranet is a Site Collection. Following that pattern you could create a Hub Site as your Intranet Root Site (A communication Site, as mentione by Chris is ideal here) and them start creating modern sites (Modern Team Sites or Communication sites) that can join the Hub inheriting navigation and theme from the Hub
2) The reason you see more WebParts in a modern team site is because that kind of site is connected to an Office 365 Group so you have connectors feature there that can use also in your site.
3) You can convert any classic site (be carefull, the same does not happens if you are talking about subsites) into a modern Site and additionally you will be able to add a Team to that modern site created.