First and foremost, I’d recommend you carefully read through our Terms of Service, which provides all of the details you need to know about what is and is not allowed.
If you take a closer look at section C you will find our content and conduct restrictions, and you will note that commercial software is not explicitly prohibited under any account type. That said, it can’t conflict with other users’ rights to fork public repositories.
There are no hard limits for downloads of released software binaries, though we reserve the right to suspend or throttle your account if we determine your bandwidth usage to be significantly excessive in relation to other GitHub customers. This also depends on the size of the software, and Git LFS usage: if you’re using Git LFS, then there are specific storage and bandwidth limitations on your account.
That said, GitHub staff is not in a position to offer legal advice, and we recommend that any detailed questions you have regarding your rights and responsibilities around proprietary content be directed to your own legal counsel.
Hope this helps!