1. Leave the shrimp in for now
2. Do NOT do a water change until NO2
is a ZERO then do a sizable PWC
3. No. YOur tank will still need to cycle properly. Honestly, Bio-spira is a waste of money and really does nothing to prepare the tank for long-term habbitation. You still need to let your tank cycle naturally.
As far as the tangs...how big is your tank? Rememeber that tangs are aggressive towards each other, especially when they are same species and real-estate is limited. You are best to start off with some hardier fish like a clown or two or some reef chromis. tangs, in general, should be the last addition to the tank due to their aggressive nature.
this is hardest part of this hobby...the waiting. I suggest you give your tank a couple more weeks before adding livestock. Your tank, fish and wallet will appreciate you for it.