Hello Wiz!  
I'm a newbie to machine sewing leather and experiencing the same overload of info shopping for a machine- I need to make a decision soon as the time spent researching- while important- is cutting into actual production!  I've been reading your postings and they're extremely informative- I joined this site largely because of the quality of info in your posts- thanks for the education! If I may, I'd like to pose a couple more questions... 
First, is there one machine (that you would recommend) that can handle a continuum of weights? Specifically,  from lighter weight items like denim and doe skin, up to and including  sturdy, medium weight leathers as for upholstery, belts and handbags? I will also be working with hair-on hides.  
I'm also unclear as to how to interpret the measurements regarding the thickness of the leather a machine can handle (i.e., if a machine is said to handle 1/4" the actual thickness of the working piece will be 1" where seam allowances converge and overlap).  
Again, I appreciate this site and everyone's willingness to share their knowledge! 
My best, 
Sheri