I'm not sure that Entomb is really a good fit in a Stax list. It has synergy with other cards, but the problem is that it is only good in combination with Welder or Crucible, meaning that it is sometimes dead. I think that in a Stax list like this, you want to maximize your redundancy and consistency, so you really want every card to be useful on its own.
I also think it's a mistake not to run Chalice of the Void, because all your list really has to control your opponent's artifact mana is the single Gorilla Shaman. Chalice at 0 is very strong, especially in combination with Sphere of Resistence, because it stops your opponent from breaking out of the Sphere with moxen/lotus, and of course makes your Wires and Stacks stronger as a result. Obviously Chalice can be set at other numbers, too--it only gets stronger in multiples.
You should also run Demonic Consultation, since it is a 1 mana tutor for most of the cards in your deck.
You also probably want a full set of Bazaars to dig and filter cards. It helps you find what you need and obviously has great synergy with Welder, Cow, and Confidant.
Pithing Needle, though versatile, is quite narrow and doesn't really have synergy with the rest of the deck. I think these slots would be better filled with actual lock pieces--if you are worried about Time Vault you can always consider running Null Rod, since it shuts off a bunch of their mana as well. You definitely need some way to deal with their artifact mana, because otherwise it's too easy for them to break out of the lock.
A good place to start would be taking a look at Vroman's build and report here:
http://www.themanadrain.com/index.php?topic=38630.0Your build is clearly different in that you are running Sphere and no Rods, but many of the same principles apply, and as I said, you may very well decide to run Rods anyway.