Ok
The tint you removed by converting to B&W is normal with digital IR. You can minimize it by shooting in raw then the first thing you do in post is adjust the color tempature to reduce the so called tint.
IR will focus differant than visible light. IE> If you shoot manual and focus tack sharp in the view finder then take the shot it will come out soft because IR is a differant wave length of light. Life Pixel conversions adjust by default the auto focus the be tack sharp but only with the 50mm 1,8 plastic fantastic lens " Unless you sent them a lens with the body to calibrate it to" The normal procedure to focus in IR is get sharp in the finder then move the foces ring a small amount determined by markings for IR on the lens, Does the 85 1.2 have these marks?
You can use your flash to light the subject just the same as with normal photography. To make the light somewhat invisible to people tape three gals over the speed light . A green red and blue, Play with combinations of gells to get desired effect , Think old school B&W filters but on the light not lens
I use a Sekonic meter when doing IR work and its spot on every time. The in camera meter is next to useless, its allways two stops or more off