Do not include code that is not compliant with your sustainable license

It is not because you have opened the access to your source code that you can now integrate in your program any kind of open source libraries. Several open source licenses have a strong viral effect (for example the GPL) that will not be compliant with your sustainable software license. Including such an external code means that you will have to fully open source your whole project and that you will not be able any more to charge it under certain circumstances.

Best Practice:
Only integrate external programs that are compliant with your sustainable software license. Do not accept contributions that rely on uncompliant libraries.

Comments:
Regarding sustainable software license, please take care of GPL programs. However you will have no problem integrating Apache or BSD like libraries.

On the other side, as the main right owner of your program, you can without any problem dual license part of it. For example you may fully open source your core kernel while keeping certain modules or extensions under a more restrictive sustainable software license.

For example you may GPLized your core framework while licensing it in the same time under a sustainable software license. Other GPL projects may then benefits of your core framework for free but will have to respect your sustainable software license if they want to use your complete project. The same is of course also valid for other type of license (Apache, BSD,...). This will allow you to participate and contribute to other open source projects while keeping a sustainable program.