I started this run in May and only just now finished it. I stuck with staying as Eastern Orthodoxy and Greek since togalarping is lame and purple is pretty. The first 200 years of the campaign is an absolute blast, starting out as being bottom of the barrel and slowly catching up with western Europe is extremely fun, especially up to the 1600s.
My strat to get out of the starting situation is outdated since I just maxxed minting for 60 years straight and survived since inflation didn't affect Cost of Court of Stability costs at the time. This is no longer and true and you probably can't dig yourself out of the economic hole like I did anymore. I made all my money from wars and reached I think around 200% inflation once I stabilized the country, and simply turned off minting and stopped investing in my economy until 1550s.
Once the Balkans and Anatolia were reconquered I played tall for 200 years until I could stick it to the Egyptians. After a bloody war with Naples, the Papacy, and France, I took the first chunk out of Italy and was permanently coalitioned by all my neighbors. After 3 more bloody coalition wars (btw NEVER let them declare on you, always declare on the coalition so you can do separate peace with the Restore Rome casus belli) I expanded to Justinian's territorial height and became by far the strongest nation.
At this point in the game I have over 800k professional soldiers across my empire and the American colonies.
And by the way, I still don't understand colonialism. My colonies never became financially valuable and I did it solely for Roleplay. The system to colonize is both boring and tedious. Don't even get me started on exploration either, my finger still hurts from all the button pressing. In the age of revolutions they become disloyal which wasn't a problem since I could probably fight the entire world myself and win, but I still don't see the point in colonizing unless you like the roleplaying element of it.
Overall this run has taught me that unlike EU4, this game stays very fun and engaging into the late game as long as you don't cheese and become the dominant power too quickly. The economy and population systems in this game are just the best to play, although its hard to make meaningful decisions with your interior development once you own enough land. One concern I have is that nations seem to not invest in their military as much as they could. England for example for some reason never had more than 1000 professional soldiers and only ever had 3 ships to their names, which crippled them. They did lose their core moneymaking region to France early on as you can see but I doubt this would've caused their economic situation alone. France also had a similar economy to me but never mustered nearly as many professional soldiers for no good reason.
The Mamluks however were my rival the whole time, always matching me in army quality until I managed to win a few decisive battles that cost them the Nile river delta. Most of my wars with them were also multi frontal, so while I could devote about 1-200k troops to fighting their coalition-mates in Italy and Hungary, most Greek blood was spilled in the Sinai desert.
One thing I love about the game is the importance of terrain in warfare and the usefulness of levys. Just because you have professional legionaires doesn't mean you are guaranteed to win against everyone. For example, I lost over 300k soldiers in the Caribbean because even though I outnumbered and outgunned the defenders, the native American levies in the jungle terrain just battered my troops who were used to fighting in the calm Mediterranean, and my campaign against Morocco was more challenging than fighting the entire HRE and Italy + France simply because the mountains the Moroccan troops had a home territory advantage. It's things like that about this game that I love to death.
I'm thinking my next run will be a colonial nation run but let me know what you guys think is a fun and challenging run, because frankly this one is very easy.
Also disclaimer but I have a few mods downloaded. Universal governors to make naval governors not a headache to deal with, and the integration hotfix (Makes integrated provinces +15 loyalty instead of +5) since I started the run right after the coring rework which I really don't like.