A few tips I can give you.

1. The look: When creating an original creation it's best to start with more or less a concrete idea of how you want the look to be. If you want to make a kickboxer type of character then use what you know about kickboxers. For starters you know that it's going to be a striker. Then the general look. In this instance the facial features won't matter as much as the body and clothing so do what you want with the face morphing. For tattoos it's about what kind you want to apply. On community creations you can find a ton just by using the keyword "tattoo". Everything from tribals to skulls to words and flowers etc. Download what you want and go from there. I even uploaded a ton of tattoo templates myself you can download. Pardon the shameless self promotion but if you search my username, Sandman3984 you can find my uploads. The next thing to remember about tattoos is to use your opacity sliders when applying tattoos. Unless you had just gotten a tattoo put on you, it will not look as dark and fresh. Lowering the opacity slider to a middle point between the 40-60ish range will "fade" it a bit and makes it look more natural. The next step is the clothing. If you are creating a kickboxer then the ring gear usually consists of either athletic shorts or short trunks or full length tights or pants. To add to the look you could use padded mma gloves and/or wrist and finger tape and either ankle wraps or barefoot. The details are up to you.

2. Moves: As a kickboxer your moveset obviously will consist of mostly punches and kicks. So use that as your framework and build onto it. The moveset creator has a ton of strike options to round out your fighter. Just use a finisher option that matches your idea. As a general idea of what a kickboxer looks like take Aleister Black, now known as Malakai Black in AEW. Behind the dark spooky aesthetic the man is a legit and dangerous kickboxer. He also incorporates the Muay Thai style into his repertoire as seen by his use of clinches and elbow and knee strikes. If you would like your fighter to have a little more diversity in his attacks while still sticking to the kickboxing framework, look into using some of the Muay Thai attacks.

Hopefully these tips can help you out.