1) No. You'd have to really carefully consider the connection geometry there to make sure you're not destroying the post with all of those connections in the same place. Besides, the influence of all the anchor rods will give you a lower than anticipated group pull-out failure. Besides - both shear walls will create tension in that post. It only needs to be resolved once. Determine the maximum uplift load in the post (consider all load cases, including bi-directional and torsional for wind). Use that to size your hold down. The precise location of the hold down will change the eccentricity in the walls and change the loads slightly, but unless you're dealing with very tall and slender walls near the high end of allowable aspect ratio, it shouldn't be that big of a deal.
2) You need whatever is required to take the tension/compression load at the end of the wall. I always require a minimum of (3)2x studs at the end of each shear wall for simplicity.
3) See number 2. And yes, if you have a point load on the wall support it like you would in any other wall.
