To buy a Subscription Plan, visit the subscription-based game's page on the Steam Store and select a Plan. Then, add it to your cart. A credit card is required to purchase Subscription Plans.
Visit Account Details, where you can edit your payment method on record or cancel a Subscription at any time. Your cancelled Subscription will remain active until the paid plan expires.
No, but you can cancel or renew your Subscription at any time.
Visit Account Details to manage your current Subscriptions, or visit the Steam Store to Subscribe again.
This depends on the game. In some cases, your game data will automatically be re-linked to your Steam account. If this has not happened, you will need to contact the publisher of the game and have them re-initiate your previous game account and link it to your Steam account. Support contact information for each subscription-based game is outlined below:
Darkfall Unholy Wars Support: https://cs.darkfallonline.com/
EVE Online Support: http://support.eve-online.com/
Visit Account Details to update your stored payment method information.
No, but a cancelled Subscription will remain active until the paid plan period expires.
Visit Account Details to review past and known upcoming charges. Some Subscription Plans are governed by the game's billing system, in which case you'll need to visit your game account for upcoming billing details. Steam will also email you billing details upon completion of every transaction.
No, not at this time.
Not for a single title, no.