Does a socket count as a magical property?
Yes, sockets count as one of the the +magical properties when crafting, Bashiok said:
Oh... and regardless of how many sockets you have, it only counts as a single affix. If an item rolls up 2 or 3 sockets, that still only accounts for a single affix spot on the item. ... Gem sockets, regardless of how many, only account for one of those 4 affixes
Check out this answer for how many sockets you might be able to get.
Yes. However, multiple sockets only count as one affix, so an item with multiple sockets can be quite a prize!