Maintenance wise the N2 and N3 are very reliable as far as I can tell. No problems that couldn't be solved up until now.
We had a few cracks at the 25° frame, but probably caused by the pilots hanging into the strap that is attached at that point to get into the aircraft, as the pilot doors are not very big.
The engines on the N3 are easy to maintain and if for any reason you have to do an engine replacement, it can be done very fast due to the great acessability. The N2 demands a little more attention because of the anticipator, but it isn't to bad eighter.
We use them for a wide variety of jobs, from offshore to hoisting to HEMS and VIP.
I know Lufttransport in Norway has NVG kits on their machines, but I think it would be better to get your information at your local Eurocopter Service Center.
Roof dinghy's are an option, but I have heared they have life rafts that can be mounted on the outside of the aircraft that serve as step. In that way you save some space on the inside.
All I can say is that the Dauphin has proven itself trough the years.
Greetz