"coding will come much later"
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Have you considered one of the many RPG maker programs? The final game might not use it but "ideas are worthless, demos considerably less so" is a thing.
Anyway what style are we looking at? Japanese, Korean, German, UK based, Russian, American?
There are some fairly key differences between most of those (maybe slightly so UK and German).
For instance Final Fantasy 6, Skyrim and the Ultima franchise. All RPGs, all radically different games. The first is a fairly trite story which you can't really deviate or role play in, the second barely has any story (would you say anybody that played the skyrim story, maybe doing one of the guilds, was getting the most of it?) and the latter has story as a fundamental component which permeates it all and allows a rather high degree of role playing. If you are not familiar with Ultima then consider the early Fallout games instead. Sometimes for these you can do them all in dialogue as well.
I am still completely bored with Final Fantasy 1-6 clones, others less so. To that end you may have to consider my words in a different way than you otherwise might. I will try to keep it at least a tiny bit generic though.
Things I don't like.
Pointless grinding. Others use it almost as a form of meditation though.
Simplistic battles. So your ice monster is weak against fire? Would be nice if there were more than about 3 of them in the game in a specific location. If I can win by pressing attack and still make enough money.
Turn based to an extent. In general game design turn based and real time are polar opposites, however I rarely have to consider many moves ahead (partially thanks to the simplistic thing above), my realistic options are limited and the menus tend to get in the way.
Forced story. Role play in my role playing game? Can I really? Will you allow it? You can do forced story (I do non interactive media all the time) but you have to do it well.
Random battles. Stick monsters on a map and have them chase me if you want. Possibly give me the chance to auto win easy battles (should be easy to do an IF some stat is greater than enemy stat then give choice of battling or walking away with XP, but maybe not harvestable/stealable items).
Some find the mechanics used to describe the world to be offputting (why doesn't the big bad which knows who I am send this mid-late game boss to flatten me right at the start? Why is the starting town filled with monsters). I can deal with that though. Weapon systems to an extent -- why my master spearman can't use a staff despite being very very similar weapons I do not know). Character classes can be tricky to do right as well -- a character might have a philosophical or physical reason to not be able to do a skill but in the absence of that please tell me why everybody does not know a basic healing spell. Also limiting things by class unjustifiably is going to be tricky -- still bitter all these years later about my monk in Might and Magic being able to learn unarmoured well enough to use leather armour but my thief not being able to upgrade that far (it had skill points and levels of mastery on top of that).
Things I like include exploration, learning systems, world lore making sense within itself (not really games but watch a few things on
https://www.youtube.com/channel/UC3ogrx6d9oohf6D42G44j1A for some of where I would be going here, if you want longer form I like
https://www.youtube.com/user/WriteAboutDragons https://www.youtube.com/channel/UCDSmC26Dr0zxiZBRWERzIFA/videos and
https://www.youtube.com/channel/UCZ_Yq-hCQ9kmCiNdDeIrbgA/videos ).
Two main types of such games
1) Power fantasy.
2) Grind you into the dirt. A few variations but roguelikes classically here and Darkest Dungeon being the current poster child of the style.
Note this is not necessarily the same thing as hard -- Etrian Odyssey is seldom described as an easy game but in the end you are saving the day.
Not suitable?
Unfairness to an extent. However the forced in game death of a character is so very poignant for a lot of them. Also allows you to balance your engine somewhat, even within the confines of a story (old master has an apprentice or group hires an old master for some help).
Surprise hidden mechanics can be something here. Hard to do those well. Far better in most cases to have a story/world reason.
Anyway this is far from a comprehensive writeup of thoughts on the matter but hopefully something of value is in this.
Xdqwerty
