I love Clip Studio, used it for a lot of years. Now that I’m pretty much entirely working on an iPad I’m torn between Clip Studio (which has an excellent full port on iOS) and Procreate. Just like you found, the default brushes are great and can be more than enough; but if you’d ever want to really beef up your brushes I highly recommend Frenden. He has probably the most extensive collection of quality brushes I’ve seen.

https://frenden.myshopify.com/

And of course, the commission looks great!