As an architect, you are going to be more than averagely sensitive to how something looks. So unless you can find a seriously large room or shed to build your layout in, you should probably rule out, for the time being, any sort of continuous run layout in 4mm scale (00).
Given your interests, I would suggest you look up a layout called Wellington Road. http://www.rmweb.co.uk/community/index.php?/topic/36589-wellington-road-leeds-1975-79-period/ You could build something similar quite easily along one wall of your guest bedroom on wall brackets or a bookcase and build it in such a way that it can be incorporated easily into any future project when you have more space. It will allow you to try all aspects of the hobby within a short timescale and see what you enjoy most.
Agree with the suggestion that you use a baseboard kit such as Tim Horn's. Given the price of good timber, if you can find any, they are a really good option.
Finally, if you want track that looks good (Code 75), you are right that your 70s models are not going to run on it without serious modification and expense. So really better to start again.
And no reason why Golden Plover, suitably renamed and renumbered, should not appear on a steam special.