Edit: yes, I realize this is probably a question based in fiction. πx10^5 BTC is rather an unlikely amount. However, my answer holds true for most any windfall, and someone somewhere might actually have a huge stash and no real idea what to do with it, or may accidentally come into one, or might just be curious what to do in such a situation. My first BTC transaction that didn’t involve a face-to-face purchase was a friend jokingly sending me 0.1337 BTC…which at the time was worth maybe a penny. So if my “leet” payment was real, why not pi?
Edit II: yes, a hardware wallet is better. However, an Ubuntu laptop that’s only connected to a network and powered on (and is therefore only vulnerable for a few minutes at a time) only long enough to sign a transaction is about as close to a hardware wallet as you can get without actually buying a hardware wallet. And of course, splitting it up to maybe 100btc per address is highly advisable…and in fact is the main reason I suggested Armory. The elliptic key system allows one single key to access an infinite number of keys, each with a small part of your stash. Also, encrypting the hard drive and making multiple, geographically distributed backups of that drive would be a damn good idea. For that matter, running it from a cdrom drive might be even more smarterer.
On to the original answer:
Last I checked, your 100,000 times π Bitcoins would be worth almost three billion US dollars. First off, you should send me a couple hundred, you know as a…umm…consulting fee. Yeah. 😉
First off for real, make sure you can’t lose them. Ask me what happened to the three ring binder full of private keys printed as QR codes that contained the $300 worth of BTC I bought in late 2009…..yeah. Don’t be that guy. Anyway, I’d recommend the original Bitcoin client on a very well secured computer, preferably a laptop running Ubuntu Linux 16.04LTS. It’s pretty much impenetrable. Make sure to lock it down per usual best practices, including the use of UFW. Then install Armory on top of that. Create a secure wallet with maybe 3-of-5 keys: that is, it’ll generate five different key segments, of which three are required to decrypt your wallet. Print them out and put them in various safe places, like safe deposit boxes inside bank vaults. Transfer all those BTC into the keys Armory spits out, maybe 100BTC to a key. This is your “cold storage,” which you can think of like a savings account. Keep that laptop disconnected from any network unless you actually need to send a transaction. Can’t hack a computer if it’s physically disconnected and powered off.
Now you gotta figure out how to actually cash them in. Bitpay has some pretty great features, and last I heard you can exchange up to US$10,000 per day. They have debit cards now too, which is pretty sweet. Coinbase is nice, but in the event that you need customer service you’re pretty much on your own. Transfer one or two BTC into whichever exchange you decide to use, cash it out or spend it or whatever, and when you need more cash transfer some more out of cold storage.
Finally, since you’re sorta kinda like a billionaire, and most people just have no clue what to do with that sort of money, get hold of a local attorney who handles things like trusts and the affairs of lotto winners. Also get hold of the wealth management department of a major and trustworthy bank. They’d be able to guide you into investments and strategies that actually make sense, unlike sending ten million bucks to some random jackhat on Quora (AKA me) or buying a fleet of Jetskis or whatever toy sounds fun today. That’s how you end up bankrupt in five years. Don’t be that guy.
In other words, treat this like you just won the most epic huge lottery jackpot in history. Best of luck to you.
And if you happen to find a plain white three ring binder with 150 pages inside, and each page has 10 QR codes on it…that is totally not worth anything, it’s definitely not my lost wallet, it’s just got a lot of sentimental value to me, my dying aunt gave it to me, please send it back. Thank you.