1.) No. Those calipers are on literally hundreds of thousands of cars of numerous marques
2.) You can do this, but they will hang down below your lower control arms and risk being torn off during normal street driving.
http://www.***************/brake-cooling-kit-replacement-hose-for-911-porsche-1969-1989.html Stock brakes should be fine until you get to either very heavy braking on the street (bad boy!) or track use.
3.) Good choices. You can even switch out the front pads to OEM style (Textar or similar) for winter use when you're not likely to get the R4-S's up to temp. Switching out front pads takes literally minutes.
4.) If the feel returned to normal after cooling off you were experiencing normal fade brought on by heat. If the spongy - ness remains, you may have boiled the fluid, glazed the pads or rotors. Step up to dot 4. Other possibilities will be addressed when you do the re-fresh.
Switching out soft lines is always good practice. Depending on use, a 5 year duty cycle is not out of order. Racers do them every season, or sometimes more often.