1. As answered above:
“Any decent web designer that you work with [should] be able to get the integration done without “losing” any parts.“
So to elaborate further, of course there’s a chance that a web designer with a low skill set or work ethic could cause you issues. But inherently, no, there isn’t anything about what you’re trying to do that instantly results in a compromise or loss of options in any way.
2. Through child theming (https://startupwp.com/topic/child-theming/) you can still utilize the options of Startup or StartupPro and essentially completely alter the look safely.
Although these are difficult questions to answer based on their subjective and speculative nature, we hope the information we’ve provided has been helpful.