Nesting Custom forms into standard pages is not a best practice as they cause caching issues. You might get call from your customers or staff regarding their form submissions didn't go through. Sometimes, its very annoying as cant trace that missing submission.
Instead, you can apply Paint Layouts on Custom forms to solve your purpose.
In addition, I would recommend to explicitly disable the cache on Custom forms through Cache manager. It just an extra step to make sure that your form will never be cached. But above suggestions still required.