I recently completed almost 20 patrols in Med, from early 1942 to mid 1944.
Here's the map with approximate positions of ships I sunk during that time:
There should be a lot of warships around, but I didn't have much luck finding them. But there are plenty of escorts.
Almost every ship is escorted, sailing in small or large convoys. Single merchants are very rare.
There's a lot of planes. Early, they cover the area around Gibraltar, Malta and Alexandria, later they are everywhere. There's also a lot of Luftwaffe early, but their presence rapidly decreases over time.
You'll find a lot of troop ships and liners. I sank six or seven 45,000t Aquitanias during these patrols, and much more smaller ones.
There's a lot of friendly ships and convoys, so identification is very important.
Your bases will eventually fall, so be prepared to sail through the Gibraltar in order to reach your new base.