Choke goes in series - it's a near short-circuit to DC, but high-impedance to your HF "noise". It really doesn't matter how you generate your 48-50v, provided there is enough filtering, & you keep audio & mains earths separated, but most off-the-shelf units will need a minimum load current to work correctly (as you say, the mic itself only draws a few mA), so may need a load resistor across the output. Thanks for the tip about µ - in return, may I offer Alt 937 for Ohm (works in MS Word, but doesn't seem to here) - in theory Alt 234 should also work, but doesn't on my keyboard