Honestly, leaving it to your hairdresser sounds like the smartest move. They deal with colour every day, and as long as she avoids the base and keeps that inch buffer you mentioned, the lace should stay safe. Testing it on an older system first is a perfect trial run.
Not aware of any place in the UK that will knot in hair, but I recall one member on a forum - probably 10 years ago - that knotted his own pieces. If you feel brave, you can buy grey and a hooking tool.
Otherwise, can you return to your supplier and ask they add grey? If its possible there will...
Be careful on any videos and their viewpoint. I would think there is a bias for click on videos to be positive of it. Just the nature of things.
My understanding, is as it needs to click on to native hair it can stress/pull those hairs (out).
If for a short term wear (eg a couple of days) or try...
The style is a good one as it obscures the front hairline which is the trickest part to get right.
If you have never used a system before then I strongly recommend you get some practice before you go on holiday. This will develop a better understanding of how to deal with a system, which in...
Compared to 12 years ago, I reduced my density and added 10% grey. I took the state of my native hair in terms of colour and density as a guide for my piece.
I use walker supertape and get 3-weeks over several washes. I know there are different strengths from daily to weeks. Maybe also chane your tape supplier and see if there is any difference. Ultimately, it could be a body chemistry and activity thing