Quote from: bigdude71 on May 24, 2017, 06:53:55 AM

1. Bitcoin block size is limited to 1 MB - right?

Right.

Quote from: bigdude71 on May 24, 2017, 06:53:55 AM

So what will happen if the amount of transactions in last 10 minutes will not be able to fit in the block?

Normally, the transactions paying the highest fees get in first, and all others will have to wait for the next block. (Miners don't have to prioritise transactions by fee, but they have a financial incentive to do so.)

Quote from: bigdude71 on May 24, 2017, 06:53:55 AM

Or for example if someone malicious will run a loop script that opens millions / billions of addresses and send them 0.0000001 BTC to clog the system...?

Without fees (making the attack incredibly expensive), such transactions will not be confirmed.

Quote from: bigdude71 on May 24, 2017, 06:53:55 AM

2. As I understand - The blockchain's ledger doesn't have my wallets total amount - it's only documenting the transactions.
So to know how much BTC my wallet has - We have to calculate everything from the beginning of the blockchain, or at least from the first block of my wallet's address - right?

Right.

Quote from: bigdude71 on May 24, 2017, 06:53:55 AM

If this is true, how come it's not super slow once the blockchain in very big?

Because wallet software stores the result, so it only has to calculate it from scratch once, which doesn't take too long in any case as computers are fast.