In my experience, in httt the OE is far more succesfull when you select a starting date somewhat later than 1399.
In my game, they owned egypt, part of arabia, the entire holy land (whats that called again?) georgia, and conquered all the way deep into russia. They kicked the crap out of the austrians (wich where huge themselves, lithuania, poland.
Only after i (Spain) declared war on them, while they were occupied with a war against Austria, Poland, Russia, and some smaller states, did they crumble. A key point in their expansion might be when they find a way around the black sea by conquering moldavia and the lands east of the black sea. blockading them no longer prevents them from moving troops around.