London Fenchurch to shoeburyness is 39 miles 40 chains (63.6km) so it would be possible to have the full route with the Dagenham dock branch and the lines through ockendon to grays and Basildon to pitsea and could have the freight trains to woodgrange park and the peak train class 387
I would suggest adding up the side branches two (I think there are three main routes on C2C) and they come to about 50 or 60 miles total?
The main line runs from Fenchurch Street to Shoeburyness via Basildon over a distance of 39 miles 40 chains (63.6 km). A loop line between Barking and Pitsea provides an alternative route via Grays and Tilbury, and there is a short branch line connecting the two via Ockendon. The line has a maximum speed limit of 75 mph (121 km/h), although the Class 357 and Class 387electric trains which run on it are capable of speeds of 100 mph (161 km/h) and 110 mph (177 km/h) respectively.