You can keep playing after you complete the monthly challenges. Making the challenges harder just makes life difficult to people with less time available than you.
I’ll probably join you guys and gals later in the month. Having got the (physics modded) Duchess Of Sutherland up and running in TSC, with 15 Matrix P3 coaches on the rear (including some sleeping cars) I’m going on tour, starting with Glasgow to Carlisle. Pretty much beats any experience TSW can offer.
This month's mastery is not that big of a chore. If I had a bit more time today I would have finished it on day one. Plenty of time left to do it this month