Not sure which instance I should post it to
The instances you speak of are actually called "communities". Instances are Lemmy servers that contain them. So lemmy.world is a instance, while !techsupport@lemmy.world is a community in the lemmy.world instance.
The desktop you suggested seem to be more than enough for very basic usage (browsing, presenting etc.). I do suggest installing Linux on them, unless you need to use Windows specific apps.