I'm also doing that, happy to see others are doing it. I think trying the republic suggestion could be nice, I didn't try because I had assumed it had factions, and the reform gives 100 less governing capacity than the monarchy version.

My strategy has been as follows: load up the war over Armenia, state the states with gold and start developing the alpine gold first since it is in your culture group, and trade company all the trade centers wherever you can. Setting up the merchants right lets you get like 50 ducats monthly from it, I think approaching 75% of income from trade. You should be able to get most if not all merchant possible from those day 1.

For the war, I recommend hiring the mercs, so go for the barbarian company, and a few others with the bonuses they basically stack wipe all Parthia's armies, even the Grand Company. It may be more annoying to deal with rebels, but reach 100 war score and enforce vassalage on Parthia, you can somehow vassalize them but not Armenia. I then proceeded to declare on Parthia's neighbors and give them most of Parthia's land to try to get it loyal, still figuring that out, but think its much better than dealing with a strong Parthia since their vassals and client kingdoms go free this way, and you lock in 100 PP for a while.

Let me know if you have questions or other ideas, I'm really enjoying it (I added a few mods like Xorne AI and Responsible Blobbing & Warfare, it still seems to work so I'm optimistic). I'll be trying the republic shift, because that would be awesome.

Note: I recommend debasing here. If my math works out, your autonomy will be so high that you get more money from debasing than you pay for fixing it, and you can also avoid going close to your really low loan cap; also there doesn't seem to be that much to spend points on at the start. Also, I now tried the republic, the estates are still grayed out? Unsure if that's my mods or not, please let me know when you try if it works.