mining adds slightly to the decentralized nature but I am curious about comparing buy and hold vs mine.
There are other benefits as well. Buying the mining rig is a sort of hedge in that if bitcoin drops to $0, you at least have some hardware that can be re-purposed/sold.
You also now have a slightly old, very special purpose computer... it is like owning a three year old graphics card in a world where you decided graphics cards are not that interesting to own... what exactly are you "repurposing" it for? If it is some really awesome ASIC-based mining rig it might only be useful to mine Bitcoin.
As for repurposing hardware, that might work with GPUs (although their value depreciates pretty quickly) but the Antminer is a custom ASIC, so it can't do a lot more than bruteforce SHA-256.
No. You don't.
The other stuff is just confusing.