The scale of the NS Design is basically the same as a full size string bass. Due to the scale of the NS Design, I suggest learning Simandl fingering (1,2,4).
Also if you plan to develop much facility you will need to learn the proper hand shape and where your thumb should fall. This guy does a decent job of explaining.
Don't get too hung up on keeping your thumb directly behind the 2nd finger. The placement of the thumb will vary depending upon your physiology and where your hand is on the bass.
Do try to maintain a nice arch and open hand position. As your hand gets tired, your hand will probably ached and collapse. Over time you will develop new muscles and learn to play with out clenching or using excessive force, so your endurance will increase over time. If possible I suggest that when you can no longer maintain a proper hand shape it's time to take a break.