Have a look at Ravensclyffe http://www.rmweb.co.uk/community/index.php?/topic/3288-ravensclyffe/ that's a very complex one man project in 8m x 4m with a 4 scale mile mainline.
So far it has taken me more than ten years and there's less track than you've got. That's DCC and computer controlled too so I understand where you want to go and have been there. Also I am now 50 years of age, I've never really not been involved with building layouts, this is the second big exhibition layout I've built on my own. I spent much of my teenage years learning with some large club layouts. You say that you've not had any real involvement in modelling since you were thirteen but as far as I'm aware you haven't told us how long ago that was.
If I was you, I would start with something much much simpler that you can get running in a short space of time, use it as a proving ground for your automation/interlocking etc.
You will never get reliable running with long trains on set-track radius curves (or pointwork!) If you want long trains then you really need to be looking at Peco streamline pointwork at a minimum, and flexible track with MUCH gentler curves.
Andi