Most softwoods are prone to blotching.

I'd recommend a good gel stain. If you decide to use a pre-conditioner, ignore the directions. They work best if let dry overnight.

Yes, temperature matters.

Here is a link that might be useful: Staining softwoods

Thank you for your help. I did read the article on staining soft wood, very interesting. I will buy some gel stain. I guess I will wait until the door is installed to stain since our garage is too cold.

To answer your question, most finishes have a critical temperature below which they will not cure, or they will cure, but not to their full strength.

The easiest finish to do is a wipe-on varnish. See link.

Choosing a finish

Here is a link that might be useful: Finishing for First Timers

I would recommend hanging then then poping the hinge pins and stain them in the house over plastic drop clothes, after the poly top coat(or whatever you use)rehang them, thus reducing the handling as a whole unit