The following may not be accurate, but I'm continually updating it as I find more information! Anyone who is more privy than I is quite welcome to kick me in the shins and fix my mistakes.
So far, it looks like there's a software module/element inside Samsung ROMs (So even if you have a compatible phone, you'll aparently be out of luck if you're running something like ParanoidAndroid or CyanogenMod). It also requires Bluetooth 4.0 LE, which is only in a few devices right now (But that number will grow). If your device doesn't support Bluetooth 4.0 LE, you're out of luck. Period. Buy a new phone if you want to use a Galaxy Gear.
The good news is that it's mostly software - the required hardware is becoming standard (but isn't yet). Theoretically, it should work with many Android phones as long as they run Android 4.3+ and support Bluetooth 4.0LE. The bad news is that someone needs to identify and reverse-engineer this software in order to plausibly enable the Gear to work with other devices.
I'll update this answer as more information becomes known.
But for the rest of your question (about ADB).
This article indicates that you can enable ADB mode on the Galaxy Gear itself, which is actually kind of exciting. The steps are simple. The article also has a helpful video!
- Swipe to "Settings"
- Scroll all the way down to "Gear Info"
- Enable "USB Debug"
If you're on Windows, you'll doubtlessly need the Samsung USB Drivers. But other than that, you should be pretty much set!