If this is not set, the current skin (at time of using the command) will be retained. You can use /npc skin -l (a lowercase L) to always use the latest skin for the player (updating if the player changes their skin). Also, if you hover over a skin, it will begin to rotate so that you can see the front and back. You can use the right and left arrow buttons to move between each group of skins. To change the appearance of the NPC, left-click on the new skin that you would like to select.
In the Preset menu at the top try out different body meshes till you find one you like. Click on the preview button at the bottom.
In the Outfit/Body menu at the top select Unified UNP HDT. Go up to the MO launcher menu and select Bodyslide and click run.
