I would like to raise the issue regarding the fortress on the hill. Perhaps it shouldn't be completely removed, as it's a fairly significant structure that plays an important role in the game! It would be quite reasonable to allow creature upgrades if a corresponding building is constructed in the castle. Someone might say, "Just take Pandora and upgrade..." but perhaps you could allow creature upgrades only for creatures purchased in the castle or only for creatures purchased in the starting castle. This, for example, could significantly help in situations where money is tight, but you need to reinforce your army and quickly pass through the fortress on the next turn.