On my needle file set, the flat file is 0.048” on the side dimension, which is fine for cutting a slot for a 0.045” G string. I’d always start smaller and expand the width, even with proper nut files, so that would be fine for getting all the initial slots cut, which will need widening on the E, A and D strings.

The nozzle cleaner files have been mentioned by others as OK for cutting bass nut slots, but the sets I’ve seen don’t have the diameters for cutting slots for the E and A strings as they only go up to 1.5mm diameter (which at 0.059” is slightly too small for a 0.065” slot.

You don’t need feeler gauges to determine a good starting height for the nut blank, just a ruler. Depth of the slot (or thickness of the fretboard for an end-of-board nut) plus 5mm (maybe 6mm for a 5-string). An 0.105” string is just under 2.7mm deep, so 5mm still leaves 2.3mm space above the board, which is more than enough for fret height and clearance.

Final nut height adjustment comes after you’ve done the final nut slot depth adjustments.