There are a lot of bikes with that same bolt, it is unlikely the strength of the bolt is insufficient. The bolt appears to be a custom item so it is also unlikely we could find a direct replacement. If yours breaks again it means something else is wrong and has to be corrected or the next new...
The pedal resistance is not bad, when riding with analog riders I often ride my SL with the power off. When you hit the speed limit it is obvious but only because it is suddenly all you trying to maintain 20 mph. :( Btw, mine (in Turbo set to 100/100) comes on aggresively and does not keep...
I would start with replacing the connectors with ones that are designed for the worst conditions: construction equipment. Those connectors live in water/dirt/mud/worse for years without a problem. Look for Deutsch DT connectors, they work.
"Right to Repair" implemented in Europe requiring manufacturers to provide parts for 10 years. Similar bills are going through some US state legislatures.
Not bicycles (yet) but they may well be included if this battle between manufacturers and owners goes the right way. We should have access to all mechanical and electrical service information for what we buy...
Electric vehicles use charge management systems to limit "full" and "empty" on their batteries, I expect Spec does the same. Charging is limited to 80-90%, discharge is maybe 20%, all in order to extend the life of the battery beyond its normal 600 cycles. We will probably never know just what...
The second nut does not secure anything, according to Praxxis it is only for the crank bolt to press against when extracting the crank. The second nut should not be removed.
I am running Conti RaceKings for the same idea, there are some nice trails around here but it's 6 miles of pavement to get there. They work great in dry weather but not so good when it gets wet.
Get the SL, unless you are in great shape an extra 240 watts should let her keep up. Since the level of assist is adjustable any mode can be set up for full power (the aggressiveness is different and can't be changed, Turbo comes on with a bang).
Oh, and as for removing the crank, Praxis notes *do not* remove the outer ring. It is only for the bolt to push on to remove the crank. The outer ring is sometimes a bit loose and one of mine did not seem to want to take 20 NM, Praxis wrote that 15 is ok.
I installed a 34 and although I rarely use the 50T sprocket it seems to have no trouble shifting in or out. As I do, you probably have plenty of tools but one I was missing (and bought) was a torque wrench for the chainring bolts (10 NM).
The three modes can be set to any level of assist/max power but the aggressiveness of how the assist comes in is different in each mode and is not adjustable. Turbo comes on with a bang! The SL can reach 15 mph on flat easily in Eco mode depending on how much assist/max power we specify in...