RyanKirkUK

It's toyota/trd optional part with specific MSRP. I doubt there will be high discount to it even in batch (unless it's some VERY big group buy that probably will never happen). Maybe something can be saved on combined shipping, but i doubt shipping for plastic piece to be very expensive and thus if there is potential to save enough on it.
IIRC it's part number is MS346-18001. Fensport in UK also offers it (£179.60). You can google by this part number for other sources/shops.

The general consensus of opinion was that they don't give anywhere near what was claimed and that your better off with a good manifold, tune and drop in air filter. 

I'd ring tuning developments.  If the power block is worth having they have probably tested it with their na tuning package.

You can guarrantee it means they are shite. Seriously change all four. Yoko Advan V105's or PS4s as a lot are using now. Don't worry about revving the engine as long as it's warm. 
Pressing the TC button once, disables traction control until 50km/h, then it will come back on again automatically. You can press the VSC button once to put it in Sport mode, which allows a little more slip and relaxes the stability control slightly. Three seconds to turn everything off except EBD, but don't worry about the pedal dance thing. 
Think about getting some tuition for RWD, plenty rave about the CAT driver training courses, worth doing if you haven't driven RWD before I would say. 

I haven't experienced it yet and wouldn't want to at that speed. However, I went round a roundabout and the whole car felt like it was sliding, very strange but also quite fun, usually just the back end loses grip but it felt like all 4 tyres where sliding; primacy's  don't feel safe with them at all. Some days they are fine, then other days they would just lose grip without warning and not pushing hard. 
 
Edit: Oh and welcome  

With the power these have you shouldn't be spinning up at 60 in a straight line. I've heard a few horror stories about people spinning out at very low speeds with poor quality tyres on the rear. Tyres should never be 'cheaped' out on due to it being the only contact on the road. I've had both Yokohama V105S & Michelin Pilosport 4's and would recommend both of them, the Pilotsport is the better one out the two but also slightly more costly