Writing software is hard work and many projects are doomed to fail. No need to get personal about it and attack the person unless he tried to scam people or showed ill intentions.
That said, this thread is indeed suspicious and raises red flags.

The idea is fairly straight forward, all you need is the code to sign a transaction and (separately) broadcast it which is freely available online and a little bit of logic to hook to the button.
You can hardcode your keys and target address into the code (just make sure that code is not shared anywhere) and just hook up the broadcasting functionality to a physical button. A led (or some other output) would be good to help you confirm the device did what you expected.

You can break this down into phases:
1. Sign the transactions offline on your PC or wallet, but don't broadcast them. Instead, just copy a small bunch of them to the device where they just queue up and wait to be broadcast when the button is sent and light up a green led. This allows you to skip the signing part for now while getting something working quickly. Of course, it's tedious to "refill" and is limited to the number of transactions you prepared.
2. Add signing to the device, so that it signs then broadcasts a fixed amount with each push.
3. Add more fancy logic to set the amount. Either pick from presets by pushing multiple buttons or longer push, or even control a number with multiple buttons and an 8-seg screen.

Of course. When you're using it to breakdown payments with no interest, then that's a good use for the card (assuming of course you are relatively confident you can pay it). In fact, that's almost like free money in a sense.

This is much easier done with a government controlled currency vs a decentralized one. Governments can bail them out then gradually print out more money to recover the cost (in effect making everybody using its currency pay for it). With crypto, unless it's state controlled, that won't be possible.

That sounds like the wrong reason to use it in most cases! Unless it's interest-free, you're almost always better off just waiting and saving up to make the purchase.

Absolutely! That's the price they will pay and that's what makes it a one-time thing. Once it's used, it's gone forever. Nobody will trust the currency again!

The US can't practically run out of cash as long as the world reserve currency is the USD. They can print money to pay their debts even to foreign countries. Of course that's a single use get-out-of-jail card. Because once they do that, the USD will cease to be the reserve currency.

Possibly at that point some "other" currency that is not controlled by any single government... perhaps something decentralized.

That's a very interesting metaphor!

To keep it simple, you will need to seed the device with the basic key generation logic or at least directly store them there along with the destination address. Connect it with some form of input, like a button and wifi. Whenever you push the button, say for 3 seconds, you would sign a transaction to send an amount of cryptos to your fixed target address. You can later make it customize the amount.

The benefit there is that if your hot wallet is stolen, then it won't have any cryptos on it until you send some from the warm wallet. If the warm wallet itself is stolen, then all the thief can do with it is send cryptos to you!

How about a "warm wallet" that allows you to only send transactions to your hot wallet on demand, but not to anywhere else?

If you use a credit card with some sort of reward and never carry a balance, then it's a net positive tool. You gain interest on the delayed payment and you get the extra rewards on top.
If you can't control your spending, then a simple trick you can try is to just put equivalent money somewhere each time you purchase something, so you know you got it covered.

Not all cryptos are truly decentralized!

Banks won't go away in a decade, but if crypto (or similar digital forms) take over, their market weight will diminish.

It might not happen soon, or even for current cryptos. However, it's not really a stretch to imagine a unified currency ruling the world in the near future. It will, by necessity, be decentralized since no country will willingly accept another's control over its economy. It has to happen organically, otherwise current rich countries would have no incentives to "allow" competitors on their turf. However, if it penetrates the world sufficiently, the transition would eventually happen because the need exists. It's only blocked by policies.

If you ever send it to "anybody" then assume it's been compromised. As to how to handle it, the answer is still the same. Use a hardware wallet. That way, even if all its content is stolen and you get it back with keyloggers and trojans, they still can't access your assets.
At the very least, transfer everything off the machine before sending it off and don't use it for local wallets again until you wipe it off.

True, but it's the benefits of decentralization that matter to most users than the fact that it's decentralized. If there was some way to ensure that a centralized alternative was censor-resistant and uncontrollable it would have fit that function (maybe some satellite central node that is immutable). BTC just happened to do it via the ingenious decentralized design.

Fluid reliable currency that transcends boundaries and defies limitations.

Your original question had no k2, r2, or s2!

The second equation was all 1's except for z2.

How is that? If crypto was used to directly buy goods and services, then there would be little pressure on it to be volatile!

s1=0 and r1=0
No payment needed