Hi Smiler 86
I'm assuming that you are already reading some railway mags, all of which advertise various products in all gauges. Have confidence in using the mail-order facilities as I have never had any problems. I frequently deal with Modelspares in Burnley, and East Kent Models in Whitstable. Gaugemaster carry extensive ranges of track power accessories as well as scenery. Peco now make locos of their own too, and check out their extensive range of wagons.
I, like others have been modelling for a number of years and try to use several suppliers because I believe it helps keep the hobby supported in other areas near and far.
Personally, I chose OO because I now have more room to build in 4mm, but not in "O". I also feel that having built some of my stock from white metal and/or brass kits then my fingers couldn't cope with anything smaller, so to a degree we are victims of design limitations. On balance, if you lack space in your house for a large OO layout then N gauge is the way to go, plus the fact that quality and detail is getting better all the time.
I wish you well for your project...jules