Well what I've done in terms of mapping for interiors, if I've the entire set of insides of houses on 1 map, if you are paranoid about the map limit.
As a rough example.
Also, yes, you can profit from RPG Maker as long as you don't use a single part of their resources, and your own custom scripts ect. Everything has to be by your hand, or by the hand of your development team or something.
I remember reading a document somewhere where Enterbrain said it is ok to use for commercial use, as long as you don't use the RTP or steal resources via plagiarism.
A few tips and tricks are to play other peoples' already made games and get inspiration from them. It is often you may feel intimidated and / or a lack of courage, but playing other peoples games and seeing how they unfold can really help. Becoming an adept in RPG Maker doesn't come over time, it is something you learn yourself, and you decide when to learn it.
Mapping - mapping seems to be more advanced than usual nowadays, as people are diverting to a new type of mapping called "Parallax Mapping". There is a thread which goes over it and how it is started. You should refrain from it until you have in-depth confidence you can sway your way around Photoshop / RPG Makers' Mechanics.
As for overall experience, as I said earlier, just play games other people have made. Don't try and "perfect" your game because nothing good will come of it. It will more than likely turn into a mess rather than a piece of work. Simply find your style of game design, and elaborate.
Some people like storyline based games, while others like game-play based. As a result you'd find some differences in terms of game play, so be sure to check over many genres too. The only other advice I can give you is that you cannot do everything in RPG maker, so don't beat yourself up if you can't make title screen music, but you can sprite very well.
Everyone has a strength and weakness in terms of game design. Some like writing, some like drawing, some like music composition and some like mapping. There are many approaches and different paths you can take to map out your learning curve for rpg maker. You'll know when you find your RPG Maker style because it'll start to show in your work and games.