FIRST please show the distribution block/ device in there now to show the line routing. Maybe he put the later prop valve in
1...Yes, prop valve meters rear
2...No, the firewall line is the FRONT brakes (largest section of the master)
3...I would cut a straight section, not the loops, one reason being it will be impossible to get good flare
4...Again, would like to see routing at "present" distribution block
Fittings sizes of two masters are not necessarily the same. Line fittings at cylinders, at old style dist. blocks, and hose junctions are normally "standard" 3/16 nuts, but nuts at the master and late model prop valve (factory) are almost always "specially sized."
Be sure to bench bleed the master. You can buy a kit at the parts stores for 15 bucks or so