I already have an individual apple developer program enrollment but I'm thinking of turning one of my upcoming apps into a full standalone business. It is already incorporated, so it is technically its own entity. Is there any downside to starting it on my individual account and moving it over to its own account later?
I would advise you to seek legal or accounting advice in your local area.
Many places it would be a very bad idea to sell an app that is owned by a corporation through an individual account. First you risk misrepresenting to Apple who's actually selling something, and secondly you risk that the money earned would end up getting taxed with your personal taxes instead of a corporation tax.
There could also be other drawbacks depending on your locality such as breaking VAT regulation, etc.