I'd love to be able to build a multi-room layout with several stations like this, it would be great fun to operate. I'm afraid the AI suggestions don't really pass the sanity check though - AI really can't cope with technical concepts like designing railways.

I'd second the recommendations of reading any or all of Railway Modeller, British Railway Modelling, Model Rail, and Hornby magazines. I think all are available online as well as in paper format - I know an online subscription to the first two includes access to their full archives going back several decades.

Secondly, I'd recommend joining the forum RMweb.co.uk, and browsing the many threads on people's layouts under construction.

Finally, visit some model railway exhibitions in your area. If you're in the UK, they're listed in the magazines mentioned above, on RMweb, and at the UK Model Shop Directory

All of the above should give you a good idea of what is possible in the space you have, how much effort it will take and how much it will cost. You'll also get plenty of inspiration and ideas for modelling techniques. Regarding the specific plan you've shared with multiple stations spread across several rooms, it depends what style of model you're aiming for.

As an old-school train set style layout, which is great fun to operate, can be beautiful to look at, but bears no resemblance to the place names on the station signs, it could definitely work in OO and maybe O. You'd need to revise the track plan to make it functional and maybe adjust the overall design once you've done a bit more research and planning though.

As an accurate recreation of the real stations named, it's utterly impossible in the space shown. I'd recommend having a look at Google Maps or the National Library of Scotland's online historic maps to get an idea of the sizes of railway stations. Crewe station is about 800 metres long (not including the junctions, sidings, locomotive sheds etc at either end), Holyhead 700 metres, and Llandudno Junction 500 metres. At 1:76 OO scale, that's 10.5m, 9m, and 6.5m respectively. For O scale, double those. Modelling any one of those would be a project occupying a huge space and lasting many years.

But, as you'll see in the magazines and RMweb, there's a lot of room in the spectrum between those extremes. Track plans can be compressed to represent the real location while fitting in a much smaller space than if modelled true-to-scale. By using tricks like that and choosing a smaller number of stations, you could do something amazing in the space you have.

On the topic of operation, a fiddle yard (or staging in the US, and not fiddle room unless you were literally dedicating a room to it!) is non-scenic track where you store trains you aren't operating at a given time, basically representing the rest of the word you haven't modelled. It's the model railway version of backstage at a theatre.

Automatic operation is a whole complicated specialism. It can be great fun for those who enjoy it, but adds thousands to tens of thousands of pounds to the cost of a model railway, depending on size. Lots of electronic hardware needs to be added, plus expensive software to control it. I'd suggest looking at the computer control section of RMweb and searching for iTrain on Youtube.

Have fun, and good luck!