Hi there aloha. I started just like you. I am afraid of ruining a model so I chose to do it on an all-white release of Dragon. I think it would be easier for you to try it on an all-white or if you really want to try it on a Gemini then choose a livery that is white in majority. As for the decals....someone refered me to
www.drawdecal.com....I never tried one from them though coz I'm not good in placing decals. Well.....just my opinion there......just wait for the other experts here to post
. Goodluck aloha....hope to see your pics soon.