Mine is fine, depends how low you want to go, if you want it in the weeds so to speak, then don't bother it will rub.
However a nice subtle drop as an example the top of the tyres meeting the arch line is fine.
I have ran mine for a several months now and no rubbing, though you do have to wary on very rough uneven ground as the exhaust may catch if you have it very low. I've not experienced any problems of catching, but then I stick to the roads and don't go dirt tracking in it that often.
The shot above was taken the day after it was done, and the rears dropped further than expected. So it's since been adjusted and sits a bit higher at the rear now, though they need to wind it up a little more next time I am in. Plenty of adjustment in the KW V1 kit I run though, so it's just been wound down too far.
As for 19's they are fine, if you choose the right tyre/wheel combination. I use 225x35 19" tyres on an 44 offset 8J BBS rim. The difference in circumference from the stock 18" Cupra wheels is 0.46% increase with the 19" rims.
Which means my speed at 70mph is only reading 70.32mph, not exactly what you would call massively out, most car speedometers can be out by up to 5% anyway.
Most tend to go with 235x35 19" tyres which increases the rolling circumference by 1.55% over stock 18's which will mean at 70mph they will be doing 71.08mph.