I've some free time this weekend, and was going to look into developing a Windows Phone app. I assumed there was just one standard SDK to develop with, but it appears not to be the case. Anyway, initially I tried to download the Windows Phone 8 SDK, but it wouldn't let me install it as I only have Windows 7 on my machine. Looking through Google, there doesn't seem to be an easy way around this restriction. Since I cannot download WP8 SDK, I see there is a 7.8 SDK, a 7.11 SDK and a 7.1 SDK and I am not sure which I should download. Basically, I'd like to try and write one app that will work for all of 7.5/7.8/8.0. Is this currently possible? If it is, will I be able to test my app through RDA on Windows Phone 8 devices and have the same user experience? Any thoughts or experience on cross SDK development would be appreciated.

Also, has anyone got any other guides, recommendations, websites or suggestions for an experienced developer (albeit a developer who has never touched .net) looking to get started on Windows Phone? I am particularly interested on material about how design patterns can be utilized and any other best practices when developing apps.

Bear in mind, I am running a modern machine under Windows 7 and only have a WP 7.8 HTC Mozart (it was free!) to test my applications against. Please excuse any of my newbie-ness

Kind regards,
grift.