i'll advise to get at least an 8 inch cone.
The extra money saved will be worth it in the end.
I'll also advise to stay away from krk. They are basically glorified consumer speakers, marketed towards the transition of people who want to maybe kinda get into audio production?
If you're serious about it, i'd suggest you go 8 inch and avoid KRK. You'll eventually out grow the size and that particular brand (maybe), but at least you know you can obtain speakers that will last you a life time.