How to adjust thread tension for different materials

[dgkfit]

Hello,

   Thank you all for your help in the past.  I have a 441 clone.  I have watched the video of Ryan Neal showing how to adjust thread tension.   It compares the top and bobbin tension to a tug-of-war.  That is a good analogy.   I have been sewing thin nylon fabric with thick #346 thread top and bobbin.  Lately my wife has bought lots of leather to make purses with.  And, she wants me to sew them.  Do any of you have some advice on how to adjust from the 346 thread down to 138 thread, and from thin fabric to thicker leather?  I of course will change the needle type and change the feed dog and presser feet?  Also, how to adjust the presser foot height?

Thanks  Dale