1. yes, it'll clear in secondary.
2. carbonation and proper temperature change a beer, as does time. would need to see the full recipe to know if there's still potential for 'thin body/mouthfeel' once its aged and carb'd.
3. headspace isn't that huge of a concern, just be gentle, no shaking...no aeration. it'll gas off some CO2 and form a blanket anyways.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10