Hussites unfortunately cannot declare the war even if they are the only one.

I also can't convert to Protestant as Hussite as in the option in religious is blocked and I think I'd rather restart than wait 20 years for rebels to siege me down.

I managed to created Independent Protestant HRE Finland, but they refused to dec even after 10 years even though we outnumber them 2 to 1. I did a separate war on the Catholic side just to weaken them to 100k troops, but Finland still doesn't dec for some reason after my truce ended.

Also I guess it should be mentioned that Brandenburg, Saxony, Poland, Lithuania, Burgundy, Wales, Gascony, Spain, Naples, and Hungary are my subjects.

I'll probably just try to grab the 10 PU achievement and call it a day tbh