Is There A Best Practice For Using Composer Packages Under The Addon?

I am developing some addons that require extra composer packages.
I know cscart already have composer packages, but it is a part of core files, so I don't want to mess with it.
What I did is init composer in the addon folder and required autoload.php file in func.php. This seems work but I am not sure this is the best practice.
Any suggestions?
Thanks.

Or register only required classes into container using service provider without including autoload.php?

Nope. not including autoload.php won't resolve namespace.

Hello
I always attach the necessary libraries to the package in the lib directory.
It seems that it would be best in addon.xml to add a function called during the installation which will download the necessary libraries.
Best regards
Robert.