If you're there already, I doubt if it will make any difference at all. If you were arriving on 29th March, that might be different but, I can't see why it would cause any problems (even if there's a "no deal brexit") if you are already in the country.
I am in Sweden, I fly back and forth due to an elderly parent. Passport, kids passports and my money - all British. I have no worries. Swedish people where I am are curious about it - there is a small 'svexit' movement up here. It'll be fine.
It depends massively on the individual countries - if one country decideds to kick up a fuss and delay planes landing / transit / take off then it will have an impact all over schedules as these days aircraft are on such tight schedules there’s very little slack in the day. Do you actually fly on the 29th or shortly afterwards? I’m sure it will probably be fine
In terms of what? Most EU govts have said nothing is going to change regarding the bureaucracy and the planes aren't going to stop working. The pound will go into freefall so change your euros back asap. When do you mean anyway? Because even the govt isn't talking about 29/3 anymore!