Soundfonts are a type of audio file created by the people who make sound blaster cards. It is originally meant for use only through those cards. And with it, you can use a soundfont to replace the standard MIDI files completely. Here's a few more details about it:
http://soundblaster.com/soundfont/
Now, SynthFont is an emulator which allows any sound card to play soundfonts. It also has some cool features that you otherwuse wouldn't be able to access within normal use like VST effects and whatnot. It also comes with Viena (which is not Vienna) which is an emulator for the soundblaster program for modifying Soundfonts.
SynthFont comes with one soundfont file, which is pretty bad. You'll have to find most of them on the web. Try
www.sf2midi.com and HammerSound to find some good ones. Sadly, most of the time it's trial and error (and some of these files are huge. It's not fun when you're a dialup user.) It will usually come as a packed .sfark file. You will need a program like sfpack to unpack them. The unpacked soundfont will have the extension .sf2
Since you haven't used SynthFont yet, it might (definitely) seem a little odd when you first open it up. I suggest playing around with some MIDIs first. After a while, it will become pretty intuitive. Just remember where you install your effects, and it should be pretty easy.
By sync, I do mean the timing. I just think it's easier to layer if at all possible so that you do have to move tracks to get one or the other at the right time.
As for lowering the voice, I don't think you will be able to successfully lower yourself an octave without some odd sounds. There will definitely be a function for changing pitch (it's pretty much a standard in all audio software it seems.) but to keep the same speed, the program has to do some adjusting to the sound. Audacity may be good at it though, you should give it a shot.