Considering that the tension on a neck is going to be somewhere around 150 to 175lbs depending on string size .... the weight of the guitar is minimal.

If you have central heat and air, the temps and humidity aren't an issue.... and really should not affect the "setup" in any significant manner.

I would opt for the forked wall hanger if you hang them flat.... that takes up more room but again, that depends on the number of guitars you need to hang. If you're squeamish about hanging them from the head stock, you can always make or buy a support kind of like a guitar stand that functions on a wall.

Of course, hanging them means you have to keep them dusted off.

Look online with a google search for wall hanger for multiple guitars..... there's lots of ideas out there... some are very cool.

Personally, I have never heard anything that says hanging a guitar from it's head stock is harmful in any way whatsoever. If it was harmful, you can bet the stores would be doing it differently. Yet I see quite expensive guitars hanging in this manner all the time.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.