Hi, i know what brand your talking about it so bad haha. I would personally have a selection of makeup brands in your kit as a brand may do a good mascara but you might not like their foundation for example (if you get me). I have done 2 makeup courses (1 taught by bafta & emmy winners) and was told this. For example in my kit i have mac prep & prime, face & body foundation, mascaras, pencils, but i also use foundations and concealors by screenface, along with benefit mascaras, glosses, highbeam etc.
You just need to see what works best for you, but a big thing to think about is brushes, try and spend on these rather than splashing out on loadsa makeup(this can be built up over time) as brushes are your tools that will last you and need to be good quality.
Hope this helps you, good look with your makeup career x