Not all at once. Begin to ventilate the propagator more and then when you have the first true leaves bring them out if you have somewhere reasonably warm so its not too much of a sudden shock. You could leave slow growing things like begonia seedlings in for longer.

If your propagator has temperature regulation you could gradually decrease the temperature over a couple of weeks.

Yes, provided the area they are then grown in doesn't go below 50'f.

Many thanks.