Go with the kit first, when you are used to it, you will know better what colors to use and even mix your own. I never use genesis, but I know the colors names are not always the same.
And the kit come with all medium you need, so after all, it’s less expensive than buy all bottles separately. Some of them, you may not like.
For exemple, I don’t like their dilutent, I use Liquitex matt medium fluide instead.