The power ribbon to the modules is most important. The -12V on the busboard should only be connected to -12V on a module. Twisting the ribbon and getting it wrong can do serious damage.
Other than that, the general advise is not to connect the output from one module to the output from another. But I have done exactly that myself, by accident, countless times when patching. The patches didn't work, but I have never done any damage to a module. I believe it was more of an issue with older modules. Newer modules are expected to be able to handle output to output.
I have also never had problems with voltages outside specified ranges, i.e., patching a negative voltage, say from a bipolar LFO, to the 1V/oct input on an oscillator that requires a positive voltage, or patching a 10V CV to an input that maxes out at 5V. It may not work as intended, but no damage is done.
Other than the power ribbon, don't worry, patch away ... :)
[edited for typos]