It comes from my experience that most ppl who do not know about RM rarely care about being RTP or not.
So, if your aim is not about impressing the veteran RM users, then don't feel bad about using RTP. Even if you pull "The Hotblooded Teenager saves the world again" type of RPG with all RTP, the casual audience will eat it up (based on my exp). Just make a bug free, completed game and see for yourself
Okay, I actually haven't "tested" it thoroughly, but if a person sees two games with the same graphics, indifferently if talking about RM games or not, what do they think? I remember when TLoZ:Majora's Mask came out, first thing I saw about it was a review where the only thing between TLoZMM and a perfect score was that all assets looked the same as its predecessor (and well, it ended up in a "98%"). Because TLoZMM and OoT look almost the same. Right?
But I don't know, maybe people just don't see enough RM games.
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As for the OP's question. If you're going to start off develop an "art" skill, you better start off thinking of it as what it is. There is no "face maker job", you start drawing, and doing digital artwork stuff. Just grab a pencil and start drawing. I would suggest to start off learning to "draw", and not learn "to draw persons/manga/whatever specific thing". But as I'm not you, I'm not going to say anything. Just care about learning general concepts like line quality (their shapes, thickness, transparency), about textures... And when drawing specific things, care about proportions and negative spaces (the counterform). Learn a little about visual language.
Still, as someone said before (I think was Tsugumo at his "So you wanna be a pixel artist" tutorial), an "artist" is 99% practice, 1% genius. Practice as often as you can, and everything will be fine. Best if you care to challenge yourself often too (can I do/achieve this thing? let's see!).
And as (somehow) some people already said, know this is going to take some time... Best to start early, but it will take time to give the results you are "hoping". Actually, what are you hoping for? That's a good question to make to yourself.
Anyway, cheers,
Orochii Zouveleki