Good evening and welcome to ECN
Firstoff, if you have 1-4" conduit, you probably have a 400 amp service feeder. To determine the service capacity, you need to know the AWG of the conductors, and the insulation.
The service capacity (amperage) is based on the load, not on the sum of the disconnects.
BTW, the "existing" service is illegal if you in fact have 8 disco's.