Neither is really preferred, it just comes down to personal preference.
--midi-key-cps=4 --midi-velocity-amp=5 are useful if want to mix MIDI input with events for the same instrument from the Csound score. If you've no intention of writing score events, then the MIDI opcodes are nice, as some of them offer additional built-in features, such as alternative tunings, velocity curves etc.
A cheap and dirty way of gaining some headroom with a complex orchestra that is overloading is to just increase the 0dbfs value. To me this feels like cheating so I think it's better to build in a master gain control using a global variable that is applied to all outputs though. Personally I'm not a fan of overusing the balance opcode as it generally ends up working like a compressor and I feel compressors should be applied later in DAWs.