Pretty much all the starter advice I could give has already been offered above, so mostly I'll just say "Welcome to the Forum" and the wonderful world of G scale modelling! You'll get all the help and advice here that you could want (and more...) and there is no shortage of People Wot Know Stuff on here to answer the more technical questions. As you've probably realised, G Scale is a very broad church that covers a range of scales and styles - there are very few absolute "rights" and "wrongs", and it's your railway to do and run what you want.
One thing I will say is that when many of us were beginners (me included, guilty as charged...) there is a temptation to have a rather "scattergun" approach to buying stuff, especially things that look too good to pass up - and we all end up with a more or less random collection of stock from various countries and lines... which is all just fine if that's what you want (unlike some of the smaller scales, no-one is going to throw a hissy fit because you're running American wagons behind a Swiss loco if you're happy with that!) - but as we progress, for many of us our interests tend to become a bit more focussed, and we gradually shed any stuff that doesn't fit a particular area of interest - if you know from the start that you have a keen interest in a particular country's railways then it can sometimes help to keep to that theme from the off, and try to resist "random" purchases...
Above all, have fun, always remember we're all just blokes playing with toy trains, and ask anything you want to - the only stupid question is the one that goes un-asked!
Jon.
