Hi Gethin,

Nice job with this.  I don't know much Japanese but I can help you a little bit.

You don't need to start every sentence with "Watashi wa"- only the first one. The particle "wa" changes the subject, sort of like "as for" in English.  So "Watashi wa" means "as for me."

I want to learn Japanese! :D

Konbanwa,(Good Evening)
Watashi wa Xtasis, Gethin desu.(I am Gethin Xtasis.)
Watashi wa (I) Artist desu! :D
Nihongo o benkyo shimasu.(I will study Japanese) use the particle "o" for direct objects.  "shimasu" is the form you would use in polite speech (i.e., where you would use "desu").
33 "(san jiu san)" sai desu. (I am 33)
Choose to be, otoko no ko (Male).
was born onna no hito. (Female).
Please forgive me for butchering the utsukushii (beautiful) Nihongo. (Japanese Language)
Hajimimashite (Nice to meet you)
Watashi Wa (I) want to make tomodachi (Friends)
Arigato Gozaimasu (Thank you very much.)

That's all I've got.  I used "Dr. Moku's" app for learning Hiragana and Katakana.  Then I started reading through "Tae Kim's Guide to Japanese" and the textbook "Genki."  Good luck!