Should we always have a niche?

I am starting my own business. I am a solo entrepreneur for now. I organize philosophy workshops for children. I just started.  I heard Brooke once say that you should always dream big–it is the process of achieving one small dream (you get the idea).  Anyway, I have 2 clients paying monthly subscriptions.  In the meantime I have plenty of ideas related to activities for children (philosophy workshops, writing workshops etc.).

So, if I am dreaming big, I am seeing myself managing a company that employs many workshop facilitators around many countries that will lead the workshops in classes while children will have access to resources online that will allow them to connect with children around the world for different activities. I will offer training to my employees.

My questions or my fears are :
– my employees : when they will get my clients, they can leave with them, overall if they are in another country. How do you make sure that you keep your clients when they represent you (eg. the life coach with coaches that can create their own company and leave the life coach)
– should I just focus on one activity at first? Philosophy workshops and then test the other activities? Should I do it by myself first and then expand by hiring? (eg. did Brooke start with a niche? Like coaching on weight loss and than expand?) or she always had one offer for all?
Because my niche can be activities for children, which large or philosophy for children.  On my website, I offer different activities with different pricing. I was thinking maybe I should offer one pricing for all the activities.

Currently, my main focus is to develop philosophy workshops but I am working here and there on other activities trying to see if there is an interest.  I am looking here for understanding my mind (coaching) but also having your opinion in a strategy in developing my business.