Tataki beef is easiest to do using sous vide technique but if you can pan fry a steak you can make it.
Sous vide temperature should be just under your target temperature.
116-118F for bloody rare
122 for rare - end target 125
128 for medium rare - end target 130
133 for medium
More than medium you don't need to learn sous vide. Just cook your beef as you always have. Consider trying it done less sometime if you are feeling brave. You are missing out.