Racers may have up to 6 Pokemon on hand as usual, whether or not those Pokemon are pulling the sled or battle-capable (or eggs), unless they need more than 6 Pokemon to be able to pull the sled like old man Junzo.

In that case the 6 Pokemon limit is waived for their sled team (but they will not be able to have any additional Pokemon on hand, only whoever is on their sled team).