I have a few questions are starting an assortment of herbs from seed. The herbs I have are Oregano, Basil, and parsley. I ordered all from Diane's Heirloom Seeds.

Just tonight, I planted the seeds in some peat pellets in a 36 cell plastic greenhouse.

1)How long should I grow out seedlings before transplanting outside?

2)Do they require the "hardening off" technique of transitioning to the move outside?

Any other tips or little notes on the subject are much welcome. Thanks guys/gals.

As for planting out--plant outside when danger of frost is gone.
Oregano is slow growing and a perennial, so you are probably not going to get much off of it this year, but it will keep you well supplied other years, because it grows like a weed.
Parsley is a biennial. That means it grows a plant the first year--the second year it flowers, sets seeds and dies. You will get parsley this year. It will winter over and next year it will send up flower stalks that look like dill. It will drop it's seeds in the fall. If you don't want the seed heads then treat it like an annual.
Basil is an annual and very suseptible to frost. You will have to plant it every year. It is very fast growing and slugs and earwigs love it. You are best to purne it early --when it is about a foot tall cut the leader branch and then keep the rest pruned too, this will help it bush out and get the leaves before the bugs do. The leaves can be cut up and air dried in the house or you can use them fresh or make pesto with them. You can freeze pesto. The basil turns a little black when frozen but it tastes good and is just as good as fresh

I hope this helps