I am not such a founder, but as a user of and contributor to open source projects let me give a suggestion of how not to do it.
If you include open source and proprietary components in the same repo I will be annoyed. Especially if it is not very clear how the licensing is split, or if the proprietary stuff is split in multiple folders.
If you don't have instructions, or it is otherwise unreasonably difficult to build the open-source only version, I will be very annoyed.
If your "open source" code is directly linked to the proprietary parts, and it requires non-trivial changes to your code in order to build without the proprietary components, I don't consider your project open source, no matter how much you plaster "open source" on your marketing materials. And it's even worse if the license is unclear on what the licensing situation is if you use a release that includes all these proprietary components, but they are turned off because you don't have a license key.
If you include open source and proprietary components in the same repo I will be annoyed. Especially if it is not very clear how the licensing is split, or if the proprietary stuff is split in multiple folders.
If you don't have instructions, or it is otherwise unreasonably difficult to build the open-source only version, I will be very annoyed.
If your "open source" code is directly linked to the proprietary parts, and it requires non-trivial changes to your code in order to build without the proprietary components, I don't consider your project open source, no matter how much you plaster "open source" on your marketing materials. And it's even worse if the license is unclear on what the licensing situation is if you use a release that includes all these proprietary components, but they are turned off because you don't have a license key.