Small layouts are “hot”. It is incredible what you can create with limited dimensions. Although a huge empire is a wealth to see, it might be also a “burden”, because it takes a lot of time …. and money!
You might opt for smaller scales, like N or Z, but also narrow gauge might be a solution! ROCO and BEMO have made several interesting narrow gauge models, in H0e (9mm) or H0m (12mm). Have a look on www.kallistoys.com / auctions and webshop to see a diversity on interesting Austrian and Swiss trains.
When are you going to start building your narrow gauge layout? Perhaps just as an extra layout!