If you want English speaking, then England's not a bad place. Other than the weather, government, local councils, exchange rate... Yeah I'm not selling this well am I. York (literally 5 mins from the countryside) does have Gigabit connectivity though. 60 mins flight from mainland Europe and 8 hours from East coast USA. Not going to happen though is it, roots go down a long way.
Its a shame the office in that video isn't for sale, because as it stands at the moment, it is divided into rooms which are not much more than a couple of cubicle spaces each. I'm not one for all this Feng Shui claptrap, but it doesn't "flow" well and they don't feel that usable. The rooms with windows in look pretty pokey too, smaller than the existing lab. It needs some of those walls removing.
I don't think you need much more space than you have at the moment, once all the crap has been dumped / Ebayed / donated. I know it is so tempting to think it is all going to be useful one day, but I'm sure local schools, amateur radio clubs and so on could make better use out of some of it. I wholeheartedly agree about light and air though. I have turned jobs down because they were in bunker type rooms. It isn't so much the S.A.D. aspect, they just make me feel like a battery hen inside some sort of soulless productivity machine. There comes a time in most of our lives where quality of life starts to be more important than standard of living, and I think now you have 2 adorable ankle-biters then it is the natural time to move on to the next stage.
TL;DR:
* Nothing beats daylight (preferably southern facing) for lighting, albeit highly variable.
* Being in contact with the outside world matters
* You don't need much (any) more space for the video side of things.
* Security issues when people find out where you are, and where $200K of test gear is stored.
* In a larger office, the studio area can be kept separate from the development and admin side of things