We have seen springs on 416 in various conditions. One trailer had them in reverse camber with no load! Others seem to be well arched. The 416 is a stout trailer and it can be abused mercilessly, including being overloaded.
I'm not so sure that's a great thing to do. The bearings are rated at a max of 1750 lbs on each side, and off road usage puts and extra stress on them, especially if they haven't been replaced or at least re-packed.
If you take the trailer mass over the 1500 lbs threshold you have to fit brakes in a lot of States. Even if your State isn't one of those that requires brakes at this threshold point it's not a bad idea for a lifted vehicle with non- stock tires. You can never get enough braking power. Electric brakes are great, are a straight forward replacement, controllable from the cab, and work in reverse as well as forward.
On the subject of spare tires, our experience has been that so long as you have an interchangeable spare between the vehicle and trailer a single spare seems to suffice. With the advent of the tire plug kits and small 12 volt compressors 99% of all flats are reparable. We have even seen side wall splits temporarily repaired using multiple plugs. Obviously peoples preferences will determine if you carry a spare dedicated to the trailer or not, as will the expedition you're on. But in general the trailer spare will not be a useful addition.