During my first playthrough, I also sailed to the sphinx. The money I received from him ran out immediately. A lot of money was spent on buying knight units in the castle and dwellings and upgrading them after transforming them into undead. I had about 20 upgraded dragons and everything else accordingly.
Added 2 minutes later
And in version 1.5, I had over 80 death messengers. However, they only started working after the gates were destroyed.