I just finished my first SDM campaign , so far my post campaign thoughts are that early game is really pain. In first 100 years I was constantly with 10-20 loans, my inflation was sky rocketing , my stability was changing from -2 to +1 almost every 2 months and event ,,Theft'' wasn't helping either with my treasury. Its hard to even keep your military most of the time, lowering maintenance to 0 still puts you around 0.20-0.70 ducats with 3 vassals and 8/8 units. In terms of wars , my first steps were to vassalize smaller neighbours , it was pretty hard even with Wallachia because I didn't see Oltenia and wasn't able to fabricate claim immediately. Second and third war were no casus belli wars against Serbia and Bosnia in which I vassalized both , that almost got coalition on my head. After all that I decided to wait a bit to lower my AE. About 15 years later when I hit my 18th loan I finally got an opportunity to go to war with Hungary , they got involved with Austro-Venician war and their troops were busy ,they were only allied to Milan. It was pretty easy to beat them up and siege with Remilia as general, I took Trontal (yay 3 base tax) and Slavonia (yay another 3 base tax) which after coring finally stabilized my economy somewhat. Sadly this war got me into a coalition of Hungary and Poland (they annexed Moldavia) so I had to wait couple of years to get out of it. Then it was pretty easy , Ottomans got HUGE rebel problems , (20-30k nationalist rebels). Albania spawned, so I immediately declared no casus belli war , annexed them , fabricated claim on Epirus and went to war with Ottomans, during that war I managed to get Byzantium and Bulgaria to spawn thanks to rebels and took Epirus + broke Ottoman vassalization of Athens. First idea group that I think is a must is diplomatic, without it you can't really annex your vassals or get out of coalitions. Getting Diplomatic Influence should be top priority to get rid of that -2 diplo relations asap.

Things I would change in current SDM state
-Remove Romanian culture from Temes and Maros and switch it to Vampire
-Start with explored Oltenia , that really impacts your first 10+ years (expedition event didn't explore it)
-Moar SDM events , less ,,Theft'' (literally lost hundreds of gold because of that)
-Nerf Flandre, 10% discipline + 15% from SDM ideas + 10% from Esprit de Corps + 15% from Quality ideas make's your army op pretty quickly with all the military points you get.

To sum it up , I really enjoyed my first campaign , it was challenging first like with any small nation with awesome Touhou flavour :D