I assume this is for your WH40K theme game. There's basically two options:
Option 1: Slavish adherence to the fiction. If the sourcebook says ten thousand fortresses with thirty lasguns and five super-heavy bolters each, then build them. You may need to boost homeworld minerals and starting Maintenance Facilities quite a bit to handle them all.
Option 2: A more modest set up that can easily be supported by a 'standard' Aurora starting race. This gives the 'flavour' of WH40K but not the numbers.
