Now that is a beautiful sling! Welcome Peppermack!  
 
There is no such thing as one optimal sling length actually. It is dependent on a number of factors. Style of throw being probably the biggest.
 
 For your height though... 32-35 inches is a good start for a lot of styles. It's really all about what feels right to you. That's where I would start though.  
 
If your planning on going with one of the shorter wind-up styles (like Apache, Greek etc.) a shorter sling will be in order.

Hello, that is a nice looking sling.  I will agree with what Morphy said about the length.  It also varies with where you are throwing, brush and wood will require a shorter sling.  The ancients carried three slings, one short, one medium and one long, they had certain things they were used for, short for accuracy, medium for all around, long for range or extra power at close range.  
 
I was told to start with a fairly short sling and work on form, most of us tried to see how far we could throw.  As we got better, our slings got longer.  After a while we started working on accuracy, the slings got shorter again.  The best ammo for a beginner is probably tennis balls,  because, sooner or later, you will hit yourself or something that you really don't want to break.  And a tennis ball probably won't send you to the hospital.  Bill