I will try to breakdown your questions:
1) When Apple's Newsstand goes away, all Newsstand apps will become standalone apps. This does not affect any functionality related to subscriptions. You can launch a non-Newsstand app today and have Free or Paid subscriptions in your app.
2) With DPS 2015 we will carry over the same retail options as previously available - i.e. you can sell a single "issue" where issue is equal to a collection. You can also offer renewable subscriptions that will entitle a purchaser to content that has been published during their subscription timeframe.
3) In addition to the standard subscription options we will also give you the capability of offering "All Access Subscriptions" similar to a Netflix or Spotify membership approach. In this scenario a user would pay for the all access subscription and gain access to all content previously published and all content published in the future as long as they remain a paying subscriber. Once they stop paying they loose their access.
4) Direct Entitlement is still a feature in DPS 2015. This allows you to entitle "print subscribers" or sell subscriptions through your website.
5) Article metering is available in DPS 2015 - This feature allows you to give users free access to a number of articles until a paywall threshold is reached. This is similar to NYTimes and other paywall news sites.
6) Android and Windows subscriptions are coming soon, but will not be available at launch.