This is just personaly opnion and you are free to build your deck as you like.
So what is your recommended numbers of grade 3s? 9? 8? 7? Do you think 6 is to little? What about 4? Is running 4 grade 3 suicide? It's all about the deck right?
CFV has blessed you with an incredible gift something Yugioh has never given you. The dark and powerfull one time use reshuffle!! Missing a grade? Reshuffle the cards you dont need. So what does this have to do with the numbers of grade 3s you run? Say you start with a hand of 1,0,1,2,2 so normal one would reshuffle 3 of those cards or only reshuffle the grade 0 and hope to draw the grade 3(you got a lot of chances anyway) But what if you only run 4-6 grade 3s? Well in that case one could reshuffel all the cards( or all except the grade that has the lowest number after grade 3 in your deck) as the cances of getting at least one grade 1 or 2 is higher.( offcourse only if you are not running extra grade 0s)
But why would one run so few grade 3s? You can not guard with them and most of them are vannlia as RGs. And to be honest you only really need one as your VG(not counting BR) Grade 3s in the hand is mostly used as sentinal feed. But you will not always have a sentinel. And 5k guard can be the difference between a win and a lose.
I personally try to run to 6 in every deck. In deck with draw power or ability to can give you the grades you need one could go down to 5-4. in my Full moon deck I only run 4 beacuse I only need the grade 1-2-3 of the ride chain. And the grade 2 will give me the grade 3 sonner or later.
In a break ride deck on would normal run 8 grade 3. I agree with this and is not against it in anyway. In a crossride deck on can get away with running 6 grade 3s if you have a way to get the pre crossride to the soul. In PBO one can go down to 5 grade 3s. Useing javlin to find PBD and use painter to get him in soul. Macha can get both painter and javlin. SP also have a good draw power so it easier to find atleast one grade 3 for javlin.
This is just my personal opinion and I would like to hear what people think about the numbers of grade 3 in decks.