No as long as you get it from the original source.
No you don't you can download it on a outdated minecraft as long as the download you download is the same as the outdated minecraft you choose
3 sec
Long grass.
As long as you get it from the Mojang website then yes it's safe.
You should be able tto download it as soon as you've paid for it.
over 9000 hours
One Minecraft block is one cubic metre. 1,000 blocks is 1km long, etc.
You can play Minecraft in your browser simply by going to the website, and next to the link you click to download the client it will say 'in browser'. Click that and you will be able to play in the browser as long as you have Java.
it wont you need to download the server thing of the minecraft website and replace the old one with it.
What do you mean by this? If you simply mean have minecraft on more then one computer then of course you can. As long as you have a valid account you can download minecraft onto any computer.
You can't play minecraft alpha 1.2.6. You can currently play minecraft beta 1.8 if you buy the game for $21.95 and then play it in the browser or download it to your computer and play it in an application. Alpha 1.2.6 is long gone, and it is not able to be found anywhere, as far as I know.