I have done waggons to era 1 limit then a little bit of acceleration , then reliability
the money in era 1 is hard to get, and the repair on CE is expensive.
Since then I maxed out waggons and acc.
now my CE looks like
20/20 railcars *maxed out*
20/20 accel *maxed out*
100% reliability *maxed out*
era 6 goods *maxed out*