The max number of bitcoin is 21,000,000
No. This isn't true. The maximum number will never be more than 21,000,000 (which is an easy number to say and remember so it is often used with the "never more than" description), but it will never be 21,000,000 either. The maximum number is less than 20999864.7679.
so the amount of transactions will pretty much slow down after it reaches that point.
The amount of transactions might speed up, or it might slow down. There really isn't any way to know.
The computing power will also get better in the future, so the blocks will be processed even faster.
Nope. Faster computing power does NOT result in faster blocks. The average time between blocks will remain at 10 minutes regardless of how fast computing power gets.
And the storage, bitcoin is real money, real money is kept in a bank.
Not always. I have U.S. dollars in my pocket. I also have some in my dresser drawer. I have a few in my car. My wife has some in her purse. None of these are banks.
What happens when a bank runs out of storage, they make more storage, and thats what bitcoin will do.
I'm not sure that your analogy makes sense, but I'm impressed by your ability to get so many things wrong in a single post.