I think you will have more enjoyment running and operating , life is short and when you get older , your health becomes an issue , get'er done ! If you got the $$$ hire a few competent fellow railroaders to help , they all will like the extra money and they are doing something they enjoy. Just make sure they understand this is work for $$$
I would base it on , I want to enjoy while I can , when you get sick and can't do anything , nothing matters. No fun when people come and see a half done layout , they all will ask , when will it be done . You got most of the tough stuff done .