Tl;dr something like Unity would be better
There are exactly three reasons not to do 3dcg for the game made in engine, designed for 2dcg.
Reason one: waste of renders. The moment you turn a perfectly solid model into a 2d picture, you lose all the potential of that model. Animation, shading, environmental lighting (discrepancies in which affect viewer's impression way more than artists tend to think). It is especially true for the RPG Maker. Any attempt at animating anything in it can only be done via god-awful live-2d, spamming scripts that show pictures on screen in correct order (which is not only as tedious as building an egyptian pyramid all by yourself, but also affects performance — and it is already far from stellar in RPG maker), or the use of gifs with pre-rendered animations — at which point one should ask themselves if there is any point to even bothering with RPG Maker anymore, as the only plus side to putting 3dcg into it instead of just making a, say, animated game in unity, is that you don't need to animate shit and trouble yourself with model collisions and what-not.
Reason two: conflicting art-styles. Which is perfectly visible from even the op-post. Realistically rendered heroines just don't fit on the same screen with cutesy-drawn slime and cartoony grass background (it also shows perfectly what I mean by discrepancies in environmental lighting). Even if background and enemies can be swapped to renders as well, you are still left with map textures, character sprites, etc etc. Do bear in mind, that switching all the default assets to pictures of models still would require making models, rendering backrounds, basically doing all the things people usually try to avoid doing by choosing RPG Maker.
And then there are issues (resolveable, yes, but present and requiring work-arounds still, only further complicating the already over-complicated scripting on Every Single Map) with the engine itself, like combat AI that makes zero to no sense unless you spend your sweet time working on every single encounter, so that player doesn't run into a monster that spams its ultimate attack every turn.
RPG Maker just is not fit for large-scale adventures, and neither it is designed to accomodate 3dcg. It does not posses any unique qualities either, aside from having its internal features (combat, movement, inventory, menus) already inside without the need to code them yourself. Hell, the same functionality can be achieved in flash, Corruption of Champions be one example. Making epic porn adventures in Maker is already like hammering a nail with a microscope, and I would strongly suggest considering another engine, better suited for your needs, before time spent on scripting tiles in maker becomes so great, that changing engine is no longer viable as a choice.
I wish more people would realise, that while you certainly CAN do a lot of things in RPG Maker, the only thing it is GOOD for is small-scale rpgs. Witch House is a good example of what RPG Maker good for, and Violated Heroine (a trainwreck of bugs and unfinished, albeit interesting, features) is a shining example of what RPGMaker can be used to do, but should not — as properly do it will not.