Hey,
1) The units of the output generated by bench should follow the documentation in the openCARP manual, section 3.1.4. This should be the same in limpetGUI plots.
2) As far as I know, limpetGUI can only be used for trace output from bench. If you want to perform tissue simulations with openCARP, there are multiple ways of visualizing the results.
There are some examples on the webpage in the section visualization. The most simple way would probably be to use meshalyzer. openCARP's output is in the igb format, which means you can also use IGB Utils to process the simulation results further.