I would a) desex him. This would help with the mounting.
b) crate train him. Give him a lovely place of his own. If you're going to keep him inside, put the crate next to your bed (cause you know, there's heaps of room what with cots and H etc!) and teach him that it's a safe place. You could let him in there when he triggers for barking, but make it nice with blankies, toys & food.
c) more walks!
d) i know it's a bit cold, but freeze some food inside a block of water. It'll give him something to do - getting the food as the water melts. Or try a treat ball - you can make one from any thick box, just make a hole not-much-bigger than food treats.
e) puppy school!
f) contact a local vet for some help

well done on rescuing a little man!