Um, traditionally, brass is mostly copper... The green verdigris that you may or may not find forming on your brass model (mostly formed due to the flux) is quite toxic and is the real reason you need to wash your hands post working on a brass kit. Once again, you'd be safer eating the solder and whitemetal than you would the brass...
I'd rather eat vegetables and a good roo steak thanks!!
I use a Dick Smith 45w temp controlled iron with excellent success, I have an old school Weller 80w iron for the bigger soldering jobs, this combination has worked for a few years now.
In the past I have always soldered as much of the white metal bits as I could. Nigel of Model Design Studio fame has suggested 5 min epoxy glue for a lot of the detail parts of his Rx kit, I quizzed him about this and he put a sound argument for glueing parts, ie, you have a longer setting time to make sure parts are square and true, you can glue little parts without fear of damage or losing other bits that have already been fixed and the glue joint of a badly located bit can be broken fairly easy (use a bit of heat as well) and reglued.
I was in a rush with the last Rx I built but I gave the epoxy a try, I am now a convert, all of Nigels points were correct, but I also found there was less clean up involved and the process went a lot quicker.
All the brass bits get soldered and the bigger white metal bits will get the low melt stuff but all the details will be epoxied from now on, on the Rx in particular, the only low melt solder will be to fix the rear of the boiler to the cab area and to solder the completed 'front frame extension' and 'coupler housing' to the chassis, these could also be epoxied on with great success. And believe me, providing the joint is clean the epoxy will
hold very well. I do believe it will speed my build time quite a bit.
I am surprised that nobody has mentioned extraction fan's, I have a little PC cooling fan set up to suck fumes away to another place other than my lungs, but I work near a window which I can open up (the fumes haven't destroyed the wire fly screen yet), it seems to work for me.