Overthinking is one of my hobbies, so I have been doing the same here. "Well, they told me I need this fish for my reef to be a success. I don't love it and it is $300." was definitely taking the fun out of it.The reality is that the majority of marine fish will end up serving some sort of utilitarian role, that being said there are for sure certain species that are utilized more than others for this purpose (tangs to control algae) is one example. In my honest opinion do your homework, get fish that interest you and are compatible with your system and just enjoy the journey. Stocking the display is one of the most fun parts of the hobby and thinking too hard about "is this fish gonna do something for the biome in my tank" can really take away from that. First and foremost this hobby is about having fun and searching for your own desirable aesthetic and functioning ecosystem.
I'm glad that folks who have been successful at this are telling me to get the fish I want. The last thing I want to do is to be stuck with a fish that I really don't like because it serves a purpose.