Hey man, i did a few runs as non-aligned Bulgaria, so i thought i might share my experience.
So the general idea sounds like that: Store 600 PP, let Zveno do their coup, so you can reject military restrictions and switch to Service by Requirement and War Economy. Spam divisions, place a new ruler, improve relations with neighbors, influence them, force Greece, Yugo, Romania and Turkey into your faction, subjugate Greece, Yugo, Turkey.
My implementation:
- Rush to Limited Women's Suffrage. In the meantime switch to Partial Mobilization (optional) and improve relations with Agrarians till they let you hire their minister. Hire Nikola Petkov and Dimitrana Ivanova.
- Go to freedom of Press. Now you have to wait till you have more than 20% of democracy support. Do not integrate Agrarians, it will boost non-aligned. Do some other focuses, but evade those, that increase Non-Aligned support. Keep an eye on democratic Party, if their support is higher than 18% after you have finished a focus - don't start a new one, wait a few days. You gonna need that PP for laws.
- So this is a part between fake democracy and civil war. So about focuses - rush to plot against Boris and prepare his assassination. Wait till Zveno prepares their coup and there is like 18 days left till it fires. Enact the decision to kill Boris, so after he dies a coup is started after a few days. It is nice to have Agrarians and NSC integrated before coup, because they give you some PP and stability, manpower, etc.
- Civil War. Refuse demilitarisation. Switch your economy law to War Economy and change your conscription law and start training some troops. You might need to wait some time to be able to get Service by Requirement, but i think it is worth it. After you'v changed your laws you have to win, try to do it in a smart way - fight only when you encircle enemy troops (best done on the bottom left part of Bulgaria) or you pin down someone so the other division can move. I do not suggest a direct push against them. Also about your construction from the beginning of the game - i usually build a few civil factories on the west (those 2 provinces that Zveno gets when the Civil war starts) and a few military factories on the east (those that i control). Civil War makes Boris reappear as a ruler, but you still have an option to go for Ferdinand or Regency Council. I prefer Ferdinand.
- Now you need to go for Guardians of the Balkan and you have to do Condemn Macedonian Organisation Focus. A smart way to deal with IMRO at the last decision would be to create a new infantry template with only one divsion. In that way when you place them at the needed positions and they get attrition you don't lose that much as you would if your normal division were staying there. While there is attrition present in those states - don't forget to remove you normal divisions.
- After that you have potential 5 Nations to influence and invite them to your faction : Albania, Greece, Yugoslavia, Romania and Turkey. Forget about Albania - Zog submits to Italy even as your Puppet, so this is a PP waste. As far as i understood - it is fine to just spam new divisions without fully training them, so that you relative strength is higher than of your neighbors. Also do not forget to improve your relations with countries you wanna force into your faction (you can guarantee a few to further improve your relations)
- So in my last game with 10 small IMRO division and 25+ normal divisions i was able to fail to force Greece(weird, they accept like almost all the time), then force Yugoslavia->Romania->Turkey into my faction. Greece declined even while having 4 green decision modifiers (Greece was thee only one i didn't influence, cause i thought it would be enough), so i declared a war against them and puppeted (with taking two historical cores back) as fast as i could. And then you can subjugate Yugoslavia->Revoke Yugo Cores->Subjugate Turkey->Try to subjugate Romania(didnt work by me).
As a result you have 4 countries in your faction, potential 3 puppets (or even 4 with Albania) before Italy declares on Greece.
What also happened by me - Romania left my faction and joined Japanese faction by some weird event/focus? Have no idea how that happend.
After all of that i justified, declared and capitulated Iran, Afghanistan and Iraq while NOT calling Yugoslavia into the war against Axis. That way you don't have to hold the front line against Germans/Italy, only to guard your coasts.
edit : typo. explained subjugation order and what to do after you'v done subjugating.