Not sure if you'll see this heare, additional note:
When the player has 0 crew, an arbitrary quantity of cargo and fuel can be carried without incuring the capacity penalty
does not happen when fleet isn't mothballed, even with a 0 skeleton crew requirement (in this case it's the fuel causing the massive penalty):
so I'm thinking:
speedrunning for exploration data/levelling is a couple of super high burn frigates preferably with solar shielding, and buying massive amounts of fuel. store all cargo/crew and go exploring.
won't be able to salvage but you CAN get exp from things, intel of where the beacons are, other astral-location data, also preliminary scans of planets. actually great for Scan missions since those don't require crew/heavy machinery.