First, congratulations on your developing interest. You will find all the information and support you could possibly want here, from information on models, to advice on building, to availability and quality of models, to historical details, you name it - just ask.
The first things to look at are what budget you have and what available space. You can fit a small shunting layout, even in 00 scale, into a surprisingly small space and all you need is a locomotive and a dozen or less trucks.
Quality varies. If you want accuracy, you need to pay a bit more. If you're not fussed about how accurate your layout is to be, anything goes and you'll get bargains at model railway shows or on fleabay. beware of customs and brexit charges from buying in Britain, though - as Broithe says, contact Wrenneire on this forum to discuss needs. If you're in Dublin or Cork or nearabouts, contact Mark's Models or call in (see them online too).
Good luck!