Starnies are a closed species~ you must have permission/a myo to make one.
Starnies have the ability to shapeshift in order to blend into any surrounding. This allows their designs to be extremely flexible! There really isn't a wrong way to design one. You can chose to have a primary form for your Starnies though a single Starnie may have as many forms as you want.
Do keep in mind a Starnie's rarity can effect their shapeshifting. Even with their shapeshifting abilities, a Starnie with all common traits can't produce legendary traits by shifting. Be sure to glance over traits so you don't accidentally use ones your Starnie doesn't have~
Starnie's can only shapeshift into living organic forms (unless they have a special trait). For example, a regular Starnie can't shapeshift into a brick or shift their fist into steel.....To be fair, they could be a plant though....
Starnies designs are encouraged to have stars or spacey elements but this is not at all necessary. There may be a limit on the number of star pieces a Starnie can summon, but that doesn't mean you can't put regular star shapes into the design~
Starnie lore should be the foundation for every Starnie, but you are free to expand upon them how you'd like~It really depends on what you want to do with your Starnie~ If you want. you can even have your Starnie reveal their true nature to the wishmaker. Their stories and choices are ultimately in your hands~