Help Starting seedlings under 150 watt for 3 weeks then putting them outside

Okay so i want to put like 30 seedlings under a 150 watt hps so there about 2-3 inches tall in 16oz cups then transplant them into 5 gallon buckets outside for the rest of the year, i want to get the plants at least 3 inchs tall so they have better chance of survival in the beginning stages.

My question is can i have the seedlings on 24 hour light or should i keep it the same as outdoors hours 18/6 ????

2.) Im thinking one 150 watt wont be enough for 30 seedlings so should i get 2 - 150 watt hps lights??

no body has any input???