The 50 should be fine, keep in mind you would ideally want small lenses that won't threaten to break open your QX1. For a wide, go get the SEL20 which works perfect with the ultra wide converter (the SEL16 is the ONLY other lens that works with the converters BTW, but it's not really that good).
Or the Sigma 19 which is cheaper, a lot sharper and only slightly bigger but doesn't take the converters. The QX1 also doesn't have the A6000 PDAF sensors so there shouldn't be any focus slowdowns with the Sigma.
You really don't need the fisheye converter unless you *like* the effect.
But really, I'd you don't shoot RAW the kit lens (SELP1650) is really good enough, especially when shooting at 16mm (this is ALREADY wider than the SEL20 + UWC).
Given a good enough location, the SELP1650 could do milky way shots just fine too - though you have to keep in mind that the
QX1 DOES NOT HAVE MANUAL MODE AT ALL (which you *kinda* need for good starfield/milky way shots).

TBH, the kit lens + the 50mm should suffice for everything you'll normally *need* the QX1 to do really.