Lets start from the beginning.
1) You have a tank, the tank must be large enough to allow the propane enough time in the ambient temperature you operate in to turn from a liquid to a vapour for the BTU you want to use.
2) You have pressure in your tank, this pressure is unusable because it fluctuates with the ambient temperature. So we add a first stage regulator. The first stage regulator stabilizes the tank pressure and drops it to a usable pressure for the second stage regulator. The second stage regulator further stabilizes the pressure and drops the pressure to a usable pressure for the appliance regulator. You get better control with two regulators but the first and second stage regulators can be combined in one housing. On a BBQ you have both first and second stage regulators combined at the tank, on some there is no appliance regulator on others there is.
3) The gas pipe, to size the gas pipe you need to know the pressure that will be in the pipe, the length of the pipe and the BTU that will be attached to the pipe.
There is a lot more to it than that but basically if you know these things you can size your tank, regulators and gas line.
The best and easiest thing to do is go to a propane supplier and have them do it, it will take them 10 minutes if they can see it.
By see it I mean the tank mount, the distance between the tank mount and the appliances and the appliance name plates.
The reason they may be telling you their regs only go up to 160,000 could be that they are two stage regs, if they go above that they go to two regs, a first and a second stage.