Welcome to the OGR forum. This really is a great place to get help with almost any issue you have with your trains. There is no shortage of opinions here... some of which are even correct.
My $.02 on the curve radius... Go bigger if you can. If you're just playing around with your RealTrax on a table or on the floor, go for it. But when you consider a more permanent layout, I'd go at least O72 and bigger if you can - especially if you might operate scale passenger equipment.
As for the advice about DCS... I would buy the system, Barry's book and the video.
Good Luck!