Revision 4 is 100% compatible to its predecessor revision 3. You CAN use revision 3 firm-/software.
However, the schematic has been pimped (even they are mostly identical).
The new schematic also is available in PDF or EAGLE (tinyusbboard.sch, tinyusbboard.brd) formats.
TinyUSBboard now also is available on an even smaller PCB.
It looks prettier, is faster to build and it is better for massproduction.
It is also cheaper, more robust and might be useful in other (kickstarter?-)projects as the center logic board.
If you are interested, please contact me...
The components are listed in blocks of recommended construction order. Total value should be less than $5.
At the moment there is no official manual for soldering the board. (It is not ready, yet.)
However there is already a lot of stuff from betatesters and fans in the net.
During construction this might help you: