I have powder coated brake masters and I have had good luck with it. It is true that brake fluid can damage powder coat, especially if you spill from the master before the powder coat has a change to properly season. But the only time I had an issue with it was when I had real issues getting a brake system to work and I spilled brake fluid on a freshly powder coated master a lot and I wasn't diligent about wiping it off immediately. It didn't fade the powder coat or melt it immediately, but i tsat on it a while and melted it so when I did get around to wiping it off.
Powder coat and let it season at least a couple days. Then wipe off any spilled brake fluid immediately - like you had just dripped it on paint - and you should be OK.
BTW, it is better if you are doing the powder coating yourself so if you mess it up you can do it again.
Can't help with the plastic window except to say you will be baking the powder coat at as much as 400 degrees. You can't powder coat plastic and I don't know when the melting/warping temperature is on that window (or its seals).
Patrick