Sure. In the pledge area there is a drop-down arrow that will allow you to change your pledge reward or add to or move rewards. Very flexible.
Each editor will be responsible for each anthology, and at the moment, no one is taking submissions. We expect that will change as things progress, so watch for updates.
No, we will not take subscriptions until this Kickstarter Project is over. Fiction River will have a web site and we will give links after Kickstarter is finished.
Don't see the answer to your question? Ask the project creator directly.