This may be a daft question but how tight do brake pipe fittings need to be. I have only ever worked with steel brake pipe so I guess the flares are much more durable than those made of copper or nickel copper pipe. I don't want to end up being Mr Gorilla and ruining the nice flares I have made !!!

How tight? Not very

In my experience bleedscrews will seal at about 6Nm hence brake pipe fittings shouldn't be tightened abouve 10-15Nm.

With copper pipes it's very easy to cut the end off the pipe by overtightening - guess how I know that

You've worried me now!

James

Try nipping them up until the unions bind and then a further 60 degrees. Operate the brakes and check for leaks, increase torque until none evident. Check frequently for seepage initially during use. This really has to come down to trial and error as it will depend on how well the flares have been formed.
As said above, be gentle, the torque required may be less than you anticipate.

Mick