The Byzantine Way [Byzantine victory over Ottomans with ~10 territories]

Try the "Byzantine Way" challenge, and conquer the entirety of the Ottomans in the 1400s scenario using only 10 provinces!
In this guide, I will discuss my method that I have tried and succeeded with.

Gameplay Basics

In this guide, I will use several in-game menus in order to find the best land to conquer. This is also optimized for the Addon + modification to the game. This would be the provinces that have

• The most people
  and/or
  
• The most economical value

I've found that the best 10 provinces for this challenge are:

• Your first 5 core territories
  
• Athens
  
• Sevastopol
  
• Sinop
  
• Both Cyprus Provinces

These provinces are the easiest to conquer that provide the best income and potential meat shields in a worse case scenario.

Lastly, there IS a exploit used involving vassalization and annexing, so if you want a purist's route, avoid the final steps of the guide.

The Nitty Gritty

Now that we know our targets, we just have to reach them.

Start your game in the 1400s as the Byzantines, obviously.
You're going to use every province EXCEPT Constantinople for conquering these other 5 territories that you don't already start with.
Begin by recruiting about 4.5k to send into Athens, the best peacedeal is that you take Athens proper and ask for war reparations from the government (which will be exiled to the Aegean Northern Isles)
This should, of course, be your second most important city. It is the only other border city you will get against the Ottomans, and will give you the best opportunity in terms of a Balkan invasion.
Buff both your Constantinople and Athens by upgrading the regular castles into fortresses. This gives a defense bonus to your troops.

After this, money is the primary concern.

Capturing Sevastopol (or in this case, Theodoro) is of critical importance.
The city has an insanely good economy for a OPM. Conquer them earlier to prevent too much military build up and prevent troop losses.

This part is a run killer.

You're left with 3 opportunities, but can only take 2 of them.

• Albania
  
• Cyprus
  and
  
• Candar

You could conquer parts, or the entirety of, any of these 3 countries.
However, I think that the best bang for your buck is to conquer the northern port of Sinop from Candar, and then conquering Cyprus. Albania opens 2 new border provinces, which means you will divert funds from the important Athens and Constantinople areas to defend them.

Albania is a ruse in this scenario.

If AI aggressiveness is higher than normal, or if you get plain unlucky, this strategy can collapse. The best case scenario is the one detailed above, but other configurations are possible with effort.

Lastly on the list of important warnings; Stabilize yourself. This should be a no-brainer, but bribing the Ottomans to a -15 relationship status allows you to NAP (Non-aggression pact) them. This will buy you valuable time. Bringing province stability to 100% on all territories is crucial during this brief period.

Byzantine Siege

Well, you've made it, the war against the Sultan begins soon.

The best chance for victory is a self-declared war, so save-scum if you feel particularly unlucky about their relationship with you.

In the brief period before war, adding armories to both Athens and Constantinople is a crucial step towards having enough troops to win the war.

By the beginning of the war, you should have about 20,000 gold saved up, which is adequate enough to win with just your fists.

Start the war with about 4000 units in Athens and 10,000 in Constantinople.
You're going to focus on the Balkans first, as it is a larger area of higher development than Anatolia.
2000 units from the capital should be sent to Sakarya, the first province in Anatolia from Constantinople. This is an easier position to hold than the capital due to the borders around Constantinople being made for potential encirclements.
The other 8000, after moving towards the Balkans via the connecting province, should be dispersed in about 3.5k and 4.5k, with the larger stack heading for the capital in Edirne.
Meanwhile, Athens should be split 50/50 on troop deployment to both bordering provinces.

If all works out, you should capture all territory listed above.

Your Sakarya units will be there for a while, so don't move them. If they get low, resupply them with about 1.5k from the capital. Feyithe is the Ottoman's sleeve trick, as it has a surprising development level and overall population. Be aware of this as your units sit in the very outskirt of Asia Minor.

Use your subsequent movement points to capture Thessalioniki and inch towards Sofia.

Both of these cities are major economic zones, and should be key priorities in the securing of the victory.

Once both are captured, clean up the Balkans and send the remaining troops to Sakarya.

The Anatolian campaign is monumentally easier than the Balkans, splitting your force down to about 1.2k, spread into the 4 neighboring provinces of Sakarya and prepare for the worst. You can eventually expand out, and finish the Sultan off. Take Byzantine corelands around the Aegean, and vassalize the Ottomans.

Vassalization = Victory
Lower their opinion of you to -10
Demand Annexation and have atleast 5000 troops.
They will submit, and you will have annexed the Ottomans with just 10 provinces.