Agree on contacting Anders, he has the most knowledge of options for extracting more power. Most of the rest of us feel lucky just to be able to keep our old cars on the road in stock configuration.
For what it's worth, I think you are very much correct in thinking that cooling upgrades are the first and most important step. More power is useless if you are not able to safely use it for more than a few seconds at a time, which is what you will wish to do for moving a large heavy vehicle. Sounds like you know this but it always bears repeating, since many people will start with a simple horsepower "goal" number, but won't put any thought into ensuring that power number is one that can be used continuously, not just momentarily. Remember that engines are often tuned for LESS hp in a higher load demand application like a heavy truck versus the same engine when used in a lightweight passenger car, so that the engine can be safely expected to operate constantly at its max power level which would rarely be used in a regular car. It's counterintuitive, but lots of people get into serious trouble when they install little engines into big heavy vehicles and figure they will make up the difference by cranking up the boost and fuel. See this thread for one example I have known personally, that led to melted pistons!
https://www.d24t.com/showthread.php?t=2015
Increasing power above the stock level in a heavy vehicle that will see constant hard use means you have to be very smart and very careful in the changes you make, and in how you then operate the truck with the extra power available, if you don't want it to quickly lead to trouble.
Cooling capability and temperature monitoring capability are the two big keys to safely running at higher power levels continuously. An upgraded or at least excellent condition/new stock radiator, high quality thermostat in a slightly lower temperature rating (many of us like the 80C Wahler or Behr units), upgraded higher flow water pump as previously mentioned, and high capacity external oil cooler are all good ideas. If your vehicle has a clutch type radiator fan, ensure the fan clutch works well and replace or upgrade if in doubt. Adding an electric booster fan ahead of the radiator is sometimes also a good idea depending on your setup and space availability. Extra power puts more heat into the pistons which are cooled by oil jets so a lot of the heat goes into the oil, thus, yes, the oil cooler's heat exchanging ability becomes more important and improvements are needed there -- both to improve heat transfer ability and, if possible, change to an external air-to-air type cooler to separate the oil cooler system from the main cooling system and keep that extra heat load out of the radiator and coolant. Finally, if you have space for it, an intercooler is a good idea too.
Then, to keep track of everything that matters, adding EGT gauge, oil temp gauge, and ensuring you have a 100% functional coolant temperature gauge are all important. Then watch them all closely, all the time.
Better yet are warning systems with audible lights or alarms to alert you to coolant/oil/EGT over-temperature, over-pressurization of the cooling system, or coolant loss. Those things are all available and are good ideas if you want to really have all the tools to protect your engine and your vacation.
In sum, your best approach would be to do cooling and gauge upgrades first then start cautiously increasing power level second.
I don't think you would need the 12mm injection pump for the power levels you are considering. In fact I think it would be counterproductive, too much fuel and hard to tune for good driveability and thermal control in your application. The stock 10mm pump can easily achieve 150 hp or more before causing any kind of bottleneck. Your limiting factor in your situation will always be cooling capability, not fuel delivery. The stock engine, turbo, and fuel pump will be able to generate more heat than your cooling system can get rid of. Carefully balancing that rate of heat output to heat transfer be your most important task.