Here's my second and final attempt (switching to Traktor) at a MF3d mapping for Serato. Below is the text from the readme included with the zip. There are also images that make everything pretty obvious, and a mfs file for the colors that I think are best.
Link to zip file:
* In the images, if there are two actions listed for a button, the bottom text is the action performed while holding shift.
--Banks 1 & 2 - Controlling Serato decks 1 & 2--
* Shift + Cue point will set the cue point.
* To loop roll any amount, activate any loop size(s) you like, then tap the "Loop Roll 32" button when you are ready to exit the loop (and jump ahead to where you would have been in the song). If you don't want the song to jump ahead when exit the loop, just tap the button corresponding to the current loop size (i.e. the last button you pressed), which will just disable the loop. Alternatively, you can tap the Yellow Activate Loop button.
* You can browse through your loops by holding shift and using the bottom 4 buttons. The two on the left scroll left (from 9 toward 1) and the two on the right scroll right (from 1 -> 9).
--Bank 3 - Juggle Mode--
* Should be pretty self-explanatory from the jpg.
--Bank 4 - Sampler Controls--
* For each sample:
* Red button (left) is Play
* Green button (right) activates Start/Stop mode
* Shift-Red activates Hold mode
* Shift-Green activates Trigger mode
* The idea here is to generally default to Hold mode and use the Red button to fire off one-shots. When you want a sample to keep playing after you've started it (or before), you can tap the Green button while holding the Red, and the sample will continue playing as you release both buttons (because it's now in Start/Stop mode). Tap Red to stop it.
* No matter which mode you're in, you can shut off the sample by hitting Green then Red (in one motion). I find this useful to remember given that this mode switching isn't exactly intuitive, and I don't want to accidently get trapped in Trigger Mode.