Universal App Question

Hi

I have just started developing Universal Apps. I downloaded Visual Studio 2013 Express and have begun using the Universal App Templates to design an idea i have. I am using a desktop with Windows 8.1 and i have a windows phone for testing the phone app.

I saw an annoucement recently that Universal Apps will be going across, Windows Phone Store, Windows Store (Desktop, Laptop, Tablet) and Xbox One App store. Although i believe the xbox one part is later in the year.

The more stores i can get my app on the better. Thats my thoughts.

Here is my question.

Is the set up and tools i'm using sufficient to develop an app for those three stores?

OR, dos universal Apps mean, Windows 10 Store, Windows phone and xbox one store?

Will, the universal apps i develop on my Windows 8.1 machine with Visual Studio 2013 Express, work on Windows 10 desktops and laptops? (as well as windows phone and xbox one)?

Although for the xbox one part, i realise, i'll have to download some sort of Sdk that i believe is being released in the coming months.

I'd just like to clarify this. Because, if i find out i'm best to start hunting down windows 10, then i'll start down that path.

Again, i want to spread my net as wide as possible.

Regards

Conor