Starting July 30th, you will no longer be able to log in to a Curse account that was not merged with a Twitch account. If you have not yet merged your Curse account with a Twitch account, please do so here! Otherwise, your account and its content will be inaccessible.
To download the other ones you need to make a folder in the versions folder for minecraft and put the client and JSON file for the versions in there. They all need to be named the same aside from file extensions. Once you do that, you will be able to choose that version when making a new profile with the minecraft launcher.
Minecraft regularly stream on Twitch and Mixer, and although as far as I know there has not been any official confirmation around where the stream will be available, it's almost certain that it will be available on the twitch.tv/minecraft and mixer.com/minecraft channels, as previous Minecon streams have taken place on Twitch. They may also stream on YouTube.