What is the recommended project size e.g. 1280x720, if your audience is the general public? If you have a large project (several content areas) what is the recommended file size for an acceptable load time ... In other words, what file size determines if a project should be separated into multiple smaller files rather one large file?
There is no easy answer. Each HTML published project will be played in a browser or in a LMS. Both have a UI which takes up space. That means that the course can never have the full browser resolution. It depends also on the browsers/LMS themselves: how have they been set up.
Bigger resolution means bigger file size as well, but that is a different question: depends on the devices which will be used and the bandwidth. If a lot of your learners will use smartphones keep the size lower, a restriction which is not so important when the learners are using laptops and high bandwidth.