Personally I've been including at least five Trainer cards in each deck I've been running as I like having access to the extra bonuses they offer, but you're free to add as many or as little as you like
The SIR format suits his character well, and the card benefits from the general strength of Trainer supporter cards in the modern market
Though, unlike with the Ringleader, you only pick up one of the revealed cards, it's still crucial you don't miss
The only issue Metalworker has it that it's a creature and can be killed before you use it
It also lets all lands enter the battlefield untapped, which is really nice and makes this a fantastic inclusion for a lot of decks with budget mana bases
Palkia VSTAR, for instance, seems like a good candidate to be paired up with Blastoise