I have PS-CS6 and PS-CC installed on my computer and both work ok.
Yes, you can purchase the CC subscriptions anytime. Please click on the below mentioned link to see the FAQ's:
Let us know if it helps,
CS6 will not effect the CC Individual or any other files which you've created with the help of CS6. So, Go ahead and take the advantage of CC limited time offer subscribtion for induviduals.
I would also like to inform that you would be able to use CS6 and individual application on a same machine without any difficulty.
Membership Plans : Pricing and Subscriptions : Individuals.
Thank you for replies, but the thing I wanted to to make sure of is if I will be able to use cs6 on my old laptop at the same time as I will be using CSS for video rendering on my main pc if I need to as I don`t see any logic in having them both on one computer.