I am still trying to get my head around wallets and the way bitcoin works.

If I download wallet software such as "bitcoin core", can I create numerous wallets within this or is it just one wallet?

From what I have read, you can have numerous addresses in one wallet. And addresses are made from a public and private key combination? Is it possible for two people to have the same public key but a different private key of does each private key always generate a unique public key?

Say I have a wallet with 4 addresses in it: With 5 bitcoins assigned to each address. So my wallet total is 20 bitcoins. I want to buy a loaf of bread that costs 12 bitcoins (a bit on the expensive side, i know). I go into my wallet and click on the 'send' option. I type in the public key that the bakery has provided me with and send 12 bitcoins. Is this possible? If so, how does it decide which address' to take from? Does it take evenly from each address or does it start from the 1st one and when it has filled its order, it stops. So if there was 15 bitcoins in the 1st address, it would stop there?

I watched a tutorial on how to paper store your bitcoins offline. And I understood he whole process. However, I want to cold store my bitcoins on a usb stick. So I was thinking instead of printing the codes, just save them on a notepad onto my USB? Is this the best way to do this, or is there a better way?

If you wanted to split 1000 bitcoins between 1000 addresses, will you have to do there a way to only send once but have it split across 1000 addresses. Maybe if they are in the same wallet for example?

Finally, am I right in thinking, you don't actually need to download wallet software to receive bitcoins? You could just go to "bitaddress.org" and generate a random address. Write this address down. Then give the public key to someone who can then send you the bitcoins? If this is possible, how could you then spend the bitcoins?

Cheers.