I didn't need any more encounters in the swamp, in fact, I thought that the relative emptiness was a good prelude to set the mood. Just make sure to have some creepy non-combat encounters, like shadows in the water, strange noises and mist, etc. to set the players on edge. When they finally come to Anton's hut, it will seem ominous indeed.
Anton's periodic ramblings are also fantastic for setting the mood. Play up these as well as the approaching storm clouds in the days leading up to the final encounter.
The mystery of the murders was pretty easy to solve, once the players went and questioned the candy seller, but I wouldn't worry about it, because there's a lot more going on than just the murders.
If you are converting to 3.5, you will probably want to re-evaluate the suggested character levels. The final battle will be very challenging to a group of 3rd level PC's, and will probably be a TPK against anything less than 3rd. AFAIK, there's no 3.5 version of either Ju-Ju zombies or a Ghoul Lord, so you might have to make those up yourself.
I ran this in 2e, so I'm not sure what you want to do about Fear and Horror checks. There's a site out there devoted to Ravenloft, something like the Arcaneum or something, so there might be more information on that site.
