is connecting high end high power leds in series feasible and are there light quality or other issues
High power LEDs usually are strips of several LEDs in series, packaged in the same housing. You can tell when they are because the forward voltage will be higher than 3~4 volts; a single blue, violet, or white LED has a forward voltage in that range, so if your LED has a 36 volt forward voltage, I'd guess there's between 10 and 12 LEDs in series on it, and possible a few strings of those in parallel. Putting more in series isn't a problem if you can supply the requisite voltage. Note that putting more in parallel isn't a good idea, though, without giving each one its own driver; paralleling LEDs requires careful matching of their forward voltages, which is easy to do if you can test and sort tens of thousands of them, but likely impossible if you only have a handful to work with.
More of a problem is the voltage. You say you're using 72 V for two in series, but also that you don't want to go to 144 V for four because of the possibility of touching them. 50 volts is the maximum for anything to be considered extra-low voltage as defined by the IEC, and I personally wouldn't want to put more than about 30 volts on anything that can be touched. I recommend you seal these so that they can't be touched, and then put all four in series, assuming you can easily provide the requisite current at 144 V.