Castile run. 1570. Asking for tips about HRE and general tips

Hello everyone

I am playing as Castile. I am in 1570. Basically, I have being following the mission tree. I have PU Portugal, Aragon, Austria, Hungry, Naples, Burgundy and England. I have inherited Naples, Austria and Burgundy. Recently I have being elected Emperor, and I have several questions about how to get IA quick.

As far as I know, the way to get IA is to get provinces back to the HRE that are hold by non HRE members. I have done so with France and Denmark using the Imperial Ban CB, but those were few provinces outside the HRE. My main loss of IA is due to several princes not being catholic. I have managed to force religion in some of them, using standard Conquest CB on those non catholics or its allies. I even managed to destroy one Center of Reformation. But there are still a lot of non catholics. The Religious war has not triggered yet, so, apparently, I still cannot use the "Religion Unity" CB.

So, the main question is: what is my best way to get IA and pass reforms?

Also, any tip about managing the HRE as Castile is appreciated.

Also, any tip in general is appreciated (respectfully, please)

And lastly, a specific question: When should I form Spain? In other runs, I did form Spain diplomatically as soon as you can (when you reach Adm tech 10). But I read somewhere, that is better to form Spain later (about 1550) when you have more Governing Capacity in order to be able to State Aragon provinces.

Here you can download the save if you want to take a look:
https://drive.google.com/file/d/1LgOixodbTs8Kn232ormWMq9kZyacVpBo/view?usp=sharing

P.D.: I recently found this https://pdx.tools/ in case anyone doesn't know about it. You can drag and drop a EU4 Save and you can check the world in web base interface (awesome).