For a first encounter, they fought a gorgon. This ended up being an exciting encounter, in which Kyle came close to death and three of the five PCs got petrified before the gorgon died. But petrification is pretty nasty, and I'm not sure I would run such an encounter.
For the second encounter, we decided to err on the low side and see how many bugbears the PCs could take on. They killed 20 bugbears or so handily with Larissa's use of Fireball. It was slower going for the next 23 bugbears. They were starting to feel the pinch, but still going pretty strong--they could probably have killed another 20 bugbears before going down. We didn't test the proposition, though; we quit after 43 bugbears.
We took too long on that encounter, and people weren't interested in trying a third encounter. So still don't feel I have a good example on ways of making encounters both survivable, manageable, and exciting.
One thing we've discovered: Kyle has by far the least hit points of any PC in the party. This is particularly problematic because he's the PC who is second most likely to get into melee, and he is perhaps most likely to get himself surrounded by monsters.