Yes, that's the area of the configuration.h the file. I'm not an expert on the hierarchy of possible controls, but my understanding is that the values starting with DEFAULT_ are what the printer will use if it has no other guidance from pronterface or the gcode file being processed. You could do a web search on each of the labels and find numerous resources where people have worked through issues on how to set them.

The bottom line is if you try to rotate the motors too fast, they won't be able to and you'll just hear them make some noise as they jerk a bit for each step without actually moving. I'm assuming that's what is happening with your motors. If you're commanding moves from pronterface, make sure the manual feedrates in Pronterface options aren't set too high or deliberately set them lower for initial testing.

On #define DEFAULT_AXIS_STEPS_PER_UNIT {78.7402,78.7402,200.0*8/3,760*1.1} // default steps per unit for Ultimaker, first of all ignore the text that says those are default values for the Ultimaker. They may be, but everyone seems to edit the values and leave the comment incorrectly there. The source of your Prusa kit actually has a Marlin build on their downloads page. I'm not saying you should use it because it is pretty dated (2012), but it is at least available as a reference. The configuration.h file in that build uses these values - #define DEFAULT_AXIS_STEPS_PER_UNIT {53.2,53.2,3200/1.25,625} // default steps per unit for NextDay. There are web resources out there that explain how these numbers are calculated. Once you have the printer working, you'll want to run some calibration prints to validate the settings and do some fine tuning, especially on the last value for the extruder steps per mm.

The other DEFAULT_ values are the same in the nextday Marlin build. Do they work? I don't know. But I run considerably lower/slower values in my prusa from MakerFarm...
#define DEFAULT_MAX_FEEDRATE {150, 150, 2, 22} // (mm/sec)
#define DEFAULT_MAX_ACCELERATION {1000,1000,5,1000} // X, Y, Z, E maximum start speed for accelerated moves.
#define DEFAULT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for printing moves
#define DEFAULT_RETRACT_ACCELERATION 500 // X, Y, Z and E max acceleration in mm/s^2 for retracts

Again, you can always at least start with lower values until things seem to work and then increase them later.

Anyone with a Prusa I2 welcome to take over at any time.