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Wow, you've written a lot. If you keep at it, you'll learn how to play. Let's go through it step by step.
1. I don't even want to explain who Vampire Lords are and why they're so cool, because it's part of the game. Play as Necropolis and see what they can do.
2. The trick with the Titans' Thunder is that without using mana or other upgrades, we get a powerful force for any hero. If we have real troops, then we don't need a 600-damage lightning bolt, and then the Angel Alliance is the best option.
3. To avoid walking for 7 days, you need to fly and jump instead. For this, we need heroes with air magic and the Dimension Door spell.
4. There are many castles on the map, so after capturing one, we can continue our journey by hiring a hero there and equipping him with wings. This is already a turn management technique that needs to be mastered.
5. To capture a Conservatory of any size, 12-15 Vampire Lords and good stats will be enough. Another option is Grindan + mass slow + Titans' Thunder.
In general, it's good that you're starting to think in the right direction. But you started a little bit from the wrong place. To learn how to play, you need to play several tournaments and study the strategies of the winners. Many things will become clearer.