Get some Wiseco pistons & Scat rods, 0.6mm headgasket, new oil pump, water pump, engine gasket kit and build it back up Leave the head it don't need touched.
The gasket bore should be 0.5mm larger than the cylinder bore. You would be pushing the boundaries using OEM gasket 1.4 bar, but that depends how well the head is clamped down.
Cusco, won't make any noise if you bed it in properly. If you plan on tracking the car helical diffs are rubbish, unless it's a Wavetrac diff but I don't think they do them for Starlets.
Yeah it will, but the more stress you run the engine at, the better control of the engine you're also going to need. If you can afford to switch, then do it, but if not then the blue will be fine.
Remember the turbo can only be as good as the air pump before it
Don't forget also this is on a .63 rear housing, unfortunately Tial don't do anything smaller and this size housing will flow enough for 550bhp ish.
Some wise choice of parts, good ecu and good map will probably knock 200-300rpm off that I reckon.
Any good quality Dot 4 fluid will suit your needs. SL6 specs don't seem too bad, not a million miles away from Type 200. Type 200 : Dry boiling point - 280 degrees C Wet boiling point - 198 degrees C SL6 : Dry boiling point - 265 degrees C Wet boiling point - 175 degrees C SL6 will require changing more often, but in fairness if the brakes get abused I'd probably say change the fluid every year anyway.