Help for an Experienced Beginner

Hi - I am a quilter normally but, in the distant past, I was a garment maker. I even took a tailoring class once and made a suit. But that was long ago and far away. I have a lovely length of wool that I found in my fabric stash and I bought the Woodland Stroll Cape for that fabric. I am awaiting delivery of some Liberty Tana Lawn for the lining and also some leather buckle closures instead of buttons. Now, I have questions: First, interfacing: I have a lot of unbleached muslin. Can I use that instead of lightweight iron on interfacing (which I recall very unfondly!). I am familiar with how to attach non-iron on interfacing. Just need to know what to use for it. Second, thread for garment sewing? I use Aurifil 50 wt cotton for quilting. Is that ok? Or should I get something else? Third and I think last is sewing on the leather closure tabs to the wool. Any special thing to do here? Any special thread? I know that is a lot of questions but it has been since the 1980's that I made a garment!!!