Lotsa questions. I’ll give brief answers that will be a little incomplete.

Why is mining a nessecary part? Is it only to keep the quantity of units in circulation in check? And why is that nessecary?

Transactions need to be recorded so that it is known who controls how many crypto coins. This service needs to be paid. That is done by creating new coins or alternatively by subtracting a fee from transactions. Creating new coins has the advantage that it spreads coins to people with a stake in the success of the cryptocurrency. If there was only a fee, then you would have to find some other way to get coins to the people wanting to use them.

Crypto is for transferring money outside the banking system and thus beyond the reach of the law. People buy and sell crypto coins for that purpose.

The value of coins depends on how much money people want to transfer and how many coins are on the market. If people want to transfer $10M and there are 10M coins available, then the price of a coin is $1. If there are only 5M coins, then the price is $1. People wanting to transfer money do not need to consider the price. If you want to transfer $20, you buy that amount of coins. It does not matter how many coins that is.

When miners sell new coins, that causes a little bit of inflation. That way, real money is transferred from the users to the miners. If someone holds a large amount of coins, they can extract a lot of money without having to do anything. So people will not be very keen on promoting that currency because that person can skim off the gains. That means it’s simply preferable to slowly introduce new coins to a wide audience.

People who “invest” in crypto cause a bit of deflation. They spread real money to the users but there is no actual value created.

Removing coins from circulation increases the price in a purely mechanical way. If the price rises further, they are able to make a profit by selling the coins and skimming off money from the users. That does create an incentive to promote that crypto coin. That’s why we are seeing so much crypto spam.

It’s not necessary for adoption to increase to see a profit. If other people can be convinced to buy and hold coins, then the price increases mechanically. This makes it possible to skim off more money from actual users than was spread to them by buying the coins. Obviously, that’s economically nonsense. It’s another fatal design flaw.

instead of proof of busywork? Why does it need to be so wasteful of electricity?

The record of transactions, the ledger, is public and unprotected. You could have different, competing versions of that record. The version that is adopted by the majority is adopted as the correct one. This creates a problem. It would be possible to spam the system with lots of copies of a fraudulent record. Proof of work mitigates that risk. Originally, it was an idea to combat email spam by increasing the cost of sending each mail.

A more efficient alternative would be to only allow a limited number of known entities to keep the ledger. If they attempt manipulation, they can be prosecuted for fraud. That’s basically the banking system.

But the whole point of crypto is not to do that. If governments could prosecute the people involved, then they could also be made to crack down on ransomware, drug dealing, tax evasion, and so on.

A more crypto-compatible scheme is proof of stake. Miners have to put up a certain amount of cryptocurrency as a stake. If other miners find that one is not following the rules, then they can be fined. Also, because they own a substantial amount of currency, they can be assumed not to act in ways that harms the network. That would lower the price of their crypto.

Why is it so slow? Will it ever be as fast and cheap as an osko payment?

The overhead necessary to avoid law enforcement means that it will always be slower and more expensive than mainstream systems.

Bitcoin, in particular, is just not suited for such wide adoption. It’s actually amazing how well it does actually work, considering its humble origins. Because of the amount of money that rests on its reputation and its decentralized nature, it is extremely difficult to get people to agree on updates.

Is there an equivalent fixed amount of USD that is in circulation?

No. Money is created every time someone takes out a loan and destroyed when it gets paid back. Physical currency (called central bank money) is manufactured as needed.

If you make more money, then you have a larger share of all the money in circulation. That means, you are devaluating everyone else’s savings and pretty much gaining some of their money.

And there’s some system where people who have joined through you, somehow also produce to you some small percentage of the money they mine. So, the ones who got in first are getting richer and richer out of others’ work.