If we're inventing a hole new religious group it might be better to make a Gnostic religious group instead of a Manichean one. But let's start with baby steps and make Manichean a non-heresy within the Mazdan group first. For heresies I think initially Manichean could just not have any heresies. It offers a good mix of historical accuracy and low workload for PDX.
Because the thing we all need to consider is that ideas are good, but someone will have to do work to actually turn them into reality. And the less work that is, the better the chance that it will be done.
Making Manichean a non-heresy by itself is very little work. All that's really needed is a new icon. Once you have the icon you can literally make Manichean into a stand-alone religion in less than 1 minute. So far so good. Adding a Learning bonus and heir designation is also very simple and will add no more than another minute or two. Throwing in the Buddhist ambitions is still under 10 minutes of work. But for artifacts and a unique great work it already begins to depend.
If you have all the numbers decided upon you should be done in an hour, maybe less. But if you don't have all the numbers decided on already, then the workload will no longer be trivial. And then with unique interactions with China, a new monastic order, and special heresy mechanics the workload becomes significant, so I'd say we drop those for now. Ideally they would be added too, but they're not essential and we should focus on the main goal.
So our request at this point should be limited to making Manichean a stand-alone religion in the Mazdan group (probably using a variant of the EU4 icon) and giving it some easily added extra features. We can still discuss the validity of each of the three (ambitions, Learning bonus, heir designation) in the thread.
If we want artifacts and great works to be added too, we need to first discuss them in detail and come up with specific numbers for everything. PDX can then choose to use our numbers or not, but the numbers we provide them with lower the workload even in the latter case because it provides them with a framework to build on.