How can I cut through brick to add a window?
I won’t say I'm an expert; I've worked with someone doing something similar in the past and may at least give you some guidance.

Personally, I would use a concrete saw (larger blade than an angle grinder) and/or a chisel to cut the opening. Make sure you have help as you DO NOT want to drop the removed section(s). You can use these bricks later (see below). 

Don't forget the header. I know I'm using the wrong term, but I'm referring to the steel plate that holds up the brick over the window. 

I would then use a chisel to remove the halved bricks and either turn them around or replace them with good ones from the removed section.

I would also recommend that you at least talk with a mason. They may be able to replicate the detail work around the window with the bricks from the removed section.