I've personally used Coinbase and find it an excellent platform. Great interface, app works well and they enforce 2FA. I'm by no means an "enthusiast" but took a similar attitude to yours a few months ago, grabbed $400 or so of BTC (and some LTC and ETH, the other two currencies on offer by Coinbase) and I'm at around $2,000 in gains now, so can't complain.

I mean, given the recent and continuing rash of hardware backdoors, wouldn't that just make your premises their premises?

I am absolutely fascinated by this! I have relatively little experience at this level of computing outside of developing some pet project VMs and a bit of 68k assembly in college. Can you expound on the purpose of a NOP sled and why that specific construct lends itself to systems exposed to specific harsh conditions?

The best example I can think of is a set of instructions on a medium. You've got jumps as a normal part of programming at this level. If the address of the jump is corrupted by an environmental factor (e.g. Hard radiation), then the jump may end up in lalaland. A sled in this context would be placed at the end of and in between sets of instructions with a jump back to a safe location to restart. So a jump to an invalid location or past the instruction set would have a chance of recovering back to a valid subroutine.