The only thing that worked for my old GSD Rebel and his jumping was to cross my arms and turn sharply away from him. He didn't nibble at my clothes though (except as a short baby) so not sure what to tell you on that. I would second the PP though and say it's past time (if you haven't begun already) to work on "sit, Down, STAY" with him.
Mine is 5 and 1/2 months and does the jumping thing (not on me, I started with the arms-crossed-turn-away right away--he does like to jump on the teenagers who thought my method was "mean"). Distraction works with Odin. A ball or squeaky toy in my hand and he backs right up to prepare to chase.
I don't think what you're dealing with is separation anxiety so much as simple excitement that you are home. If he had separation anxiety, I'm guessing you'd have destroyed things in the yard, holes dug, etc. when you got home, not just a super excited pup. Maybe a leash and quick walk or a fast game of chase-the-ball would work instead of just letting him right in the house.
The peeing only in the kitchen...not sure what to tell you but I'm sure others will chime in. But overall it sounds like maybe he's not getting enough exercise. The old saying "a tired puppy is a good puppy" is very very true with these pups.
Chris, mom to:
Tank (Cardigan Welsh Corgi)
Odin (GSD 8/28/13)
Valentine-our ragdoll cat
Two great skin kids