For the entry-points mechanism, yes — that is what makes installation the registration step and gives you version metadata for free. Directory-scanning plugin systems avoid the packaging requirement but give up dependency resolution, versioning and uninstallation, which is a poor trade for anything that outlives a prototype.

Go straight to Typer unless a dependency is genuinely unacceptable. The moment a tool has two subcommands, the things Typer gives you for free — nested groups, shell completion, conversion and validation with readable errors, a test runner — are exactly the code you would otherwise write and maintain by hand. argparse remains the right answer for a bootstrap script, an installer, or anything that ships into an environment where you cannot add packages.

Yes, and it is the natural consequence of keeping core/ free of framework imports. The library is core/; the CLI is a thin adapter over it. What breaks the arrangement is letting CLI concerns leak downward — a core function that prints, prompts, or calls sys.exit is one that cannot be imported by anything else. Return values and raise exceptions; let the adapter decide how they are rendered.