Yes you can have more than 4 additional routes (I've got 57 on) - you need to install TrainStore on your system, MSTS will take every piece of route stock and activity you have into memory. Trainstore helps by just putting the stock etc you need into MSTS storing all the unused stock in a seperate set of folders. The crashes you are experiencing are for this reason, also look at the MSTSBIN patch as this improves memory handling as well and offers extra things like switchable cabs etc.
It is important that you read the readme and beginners guides at least to get started and use the simple interface first till you are more confident with its workings.
As Ryan says its important to always keep a copy of the latest Tsection. This is because older routes will overwrite this file and make newer routes useless
After I install any route to my setup I always replace the Tsection as a precaution and touch wood haven't had any major problems todate.
