Remember that you are pumping a large volume of climate controlled air out of your home with your venting (most likely.) This is very inefficient, every bit of air pumped out is now leaking in from outside and needs to be heated/cooled again, you want your vent at minimum speed that keeps temp/humidity. So don't go nuts and get a 12", lol. 4" is what 90% of the grows on here need, but 6" is used since fixtures usually use this size.
Taste is subjective, do your own side by side testing on flushing vs no flushing and cure well in either case. You will get strong feelings on either side, so no point listening, just try for yourself.
Many like to say organic soil tastes better, they taste almost identical to me when grown side by side with DWC. Again, try clones of the same plant in each medium/nute and decide what your tongue and brain think of the results.