Problem is, the oven manual seems like it’s written by people who don’t bake much. How do I know when to use bottom heat only or top heat only or both heat w/o fan?
Knowing which feature to use is probably more an aspect of cooking knowledge, rather than equipment knowledge. For instance, I cannot imagine a use for a top heat only in baking; I would only use it for broiling.
Those with convection ovens can provide guidance for when its use is appropriate in baking; I have seen warnings against its use when baking more delicate products, because of the vigorous airflow. Supposedly, too, cakes are better with bottom heat only.
While the manufacturer is ultimate authority on how to operate the oven, I think your best source on how to cook with it is other cooks.