I am fairly inexperienced with UX design so take what I say with a grain of salt.
When you say you’re not sure what UX method to use I am not sure what you mean by that. Could you elaborate on that more? UX design uses the design process to help you ideate, research, then design a potential product.
From your other two questions it seems like you are focused on being able to create a proper persona. In my opinion I don’t think every design necessarily needs a persona. The goal behind the persona is to get into the mindset of what the end user/target user would be like and what they need. The first steps should be focused on doing research on the idea and interviews to get more in depth data. Surveys could also be another method to gather data.
I think your first goal should be to get an idea of what the market is like and if an opportunities exists through research. After doing research you should be able to create personas of who you think the audiences are. If they aren’t correct then you might find that out later and have to adjust it.