A. You won't get zapped from 48VDC. If you are extremely sweaty you might feel a slight tingle, but nothing to get excited about.
2. Just wire up some big batteries in parallel and you don't have to worry about voltage drop under load. As long as the rectifiers can keep with the current needed to float the batteries at 48V (really more like 52V in practice) you're fine. As stated by an earlier poster, this is proven technology in use by telcos for a very long time.
D. This whole article is about datacenters. I hope Joe Twelvepack hasn't just slurpped down 7 Bud Lights and wandered in to wire up some servers, but if he has I doubt a dedicated power connector is gonna keep him from fouling something up. There already exist standard 48VDC connectors. They're called lugs. Just remember, the positive terminal goes to ground. Actually I have seen modular plugs for this purpose, but any tech worthy of working near such equipment should be able to terminate a color-coded cable easily enough.
When a fellow says, "It ain't the money but the principle of the thing," it's the money. -- Kim Hubbard