NE5517 LTSpice simulation questions
1) That is actually a PNP current mirror. On a chip you can, instead of drawing 2 PNPs, draw one larger one but split the collector. Just replace this 2-collector PNP with 2 normal PNPs in a mirror configuration.

2) The value is anyone's guess, it determines the value of the biasing current through Q15 and Q16. 10 mA would be a reasonable assumption so then R1 would be 0.7 V / 10 mA = 70 ohms

3 + 4) The actual sizes of the transistors is the manufacturer's secret unless you would decap an NE5517 and measure it under a microscope. But don't worry about the parameters as they do not really matter that much.

Are you aware that all the diodes are actually also NPNs and PNPs with base and collector shorted ? Where connected in parallel with an NPN it will be an NPN and the same for PNP. Like Q8 and D5, that's actually a current mirror !

The only diodes that are not the input of a current mirror are D2, D3 and D7.