You should probably pick up a digital or paper copy of Barry Broskowitz' (RIP) DCS Companion. It is basically the bible of DCS.
TIU's have a TVS on each output, but additional ones are a good idea. Across the main feed wires to each MTH power distribution block is a good spot. I personally use one also at each transformer output. You can't really go wrong with a Z4000, but your Z1000's will work fine too.
Rod