the rear spacing on my frame was 6mm wider than my 120mm hub. I used a frame alignment gauge when bending the rear so I know I have perfect alignment and 6mm isn't that much. 10mm seems like alot to squeeze and you may run into issues with your rear dropouts if they're not perfectly parallel.

If you do decide to use a longer axle and spacers you might be ok with chainline on both fixed and free if you have the same distance in spacers on both sides of the wheel but who knows if you'll be lined up with your chainring. You might have to try bolting the chainring on the inside or outside of the cranks or maybe even get a new bottom bracket.

As far as the front hub spacing - just contact your wheel builder and find out what size front they're using. I dont' remember if my front hub spacing was 96mm or 100mm.