Yeah the VTX 1300 is definitely bigger than a sportster, I sat on one a few days ago and definitely noticed the weight & size difference. I do like the sound of the VTX though, so if I find one I like at the right price I may go for it.
Regarding riding experience- admittedly pretty limited. I'm signed up for the "new rider course" at my local Harley Dealer. Like the MSF it counts as the driving portion of the DMV test and gets me an insurance discount.
I understand the merit behind the "600cc rule" for new riders, so I'm okay with a Sportster 883 or similar in the short term since it gets me the sound I'm looking for without too much power. Definitely not looking for sport bike power at this point.
As for the aviation reference, I'd of much preferred starting with the MU-2