IPhone 4S/ 5 with Straight Talk?

So, I heard that you can buy an unlocked iPhone and then have it on Straight Talk, which sounds unbelievable.
1) Does SIM card come w/ straight talk or do I have to buy it?
2) Is SIM card a one time buy or do you buy it monthly?
3) Does the iPhone 5 come w/ straight talk or is it just 4s?
4) how good is the Internet/ calling? Is the reception good?
5) Is this a good idea?
sorry for the unneeded questions I'm just really unsure as how this all works, I'm only a teenager

The sim card is just what you get from your carrier to put into your phone to make it work with their towers. I would do it because it uses T-mobiles towers, so you get good connection.

1) Does SIM card come w/ straight talk or do I have to buy it? You need to buy a phone from Straight Talk that is a smartphone. Take the sim card out and then cut it to the size of the sim slot on the iPhone.
2) Is SIM card a one time buy or do you buy it monthly? The sim card is a one time buy. You do need to use the re-fill card unless you are on a monthly plan. You'd add units per month, or pay a bill each month, but it would not be more than 45$ usually for everything unlimited.

3) Does the iPhone 5 come w/ straight talk or is it just 4s? I assume the 5 would work as well, but for success for sure the 4S does.

4) how good is the Internet/ calling? Is the reception good? Reception for GSM (sim required) phones on Straight Talk, the phone uses AT&T and T-mobile bands. So if you check the reception for them in your area and it's good, then the service and reception should be good as well too.

5) Is this a good idea? Ultimately, you'd get all of the features you'd come to expect on a fully loaded iPhone. You need to make sure though that the bands and such are set up though, if you do something incorrectly, you may end up not getting web outside of Wi-Fi or no picture messaging and ending up still having to pay for a feature you can't use.