How useful bulk will be for you depends on what type of player you are and the reason for your purchase
With how strong Vehicles tend to be, combat is a very viable route towards winning the game
Combos do exist, but in order to get to them, you might well be taking some really long turns with the amount of mana producing spells and abilities that could sit in this deck
Since most of them are resource-heavy the suggested number is somewhat low, but if you can add more without hurting your mana curve (and your wallet since low mana ones are pricey) and consistency (for the alternate win conditions) everything more is a bonus
Old Frogs Kenrith already seems to be a pretty nice fit for my Frog army, but there are some older Frogs I've thrown into the list that will work nicely with his Royal Highness
Interestingly, korvecdal is a unique term created for Magic that refers to a prophesied leader that can unite the three tribes from the plane of Rath the Kor, Vec and Dal tribes in a fight against the Evincar