Solution for 1st question:
In SharePoint Online Modern Communication Sites, you can create a main menu with Nested links & sub-links and display the hierarchy in the form of a sitemap like shown in below image:
In SharePoint Online you can create either Header (without link) or URL for navigation to another pages/documents in your site. So you can ...
you can see the entire list of SPO Plan here. I'll began with answering your question.
E3 vs F1: Both the license include access to SPO. You can consider F1 license as trimmed down license for O365, where user get access some of the services only, while the E3 license cover more services and E5 have all of them. For example, user will not access to MS Word ...
Follow below steps:
At sub-site level, while breaking the permissions from Site collection select the options to create a new group and create groups for your sub-site as given below:
Then go to the home page of your sub-site.
Select Site permissions from Settings(Gear) icon.
Click on Change sharing settings under Sharing Settings.
Toggle Allow access ...
Both Microsoft Flow and PowerApps supports Export and Import functionalities to migrate them across another tenant or another environments.
You can find the Microsoft official documentation for the same in below links:
Migrate PowerApps between environments and tenants.
Export and import your flows across environments with packaging.