A suggestion for the "art-part"
If you are not an artist, and dont want/cant affort an artist, and dont want to use free assets:
You have 2 options:
-either create a rendering method, that produces visually appealing art from very simple to create shapes
(like some fake 3D with shadowmapping and particle/bloom effects)
-> so let your technical skills define the art-style
-research and play around with a very easy to produce art-style, that you can manage (given your skill) to create
- use very low res graphics with a very limited color palette
- create a voxel renderer and make yourself an editor for it
- use simple geometric shapes and create nive looking transitions and effects or textures, something of a workflow that you can
do and redo again and again in your graphics editor
- use a vector drawing program (like inkscape), draw your art roughly as a bitmap and then convert it into vector graphics
(an easy way to create high resolution graphics from a sloppy simple base-drawing)
-> add some effects to it too
anyway, play around with a WORKFLOW that allows you to have a coherent art-style without the need
for a lot of artistic skill.
what you dont want to do is spend lot of time to create a single asset, then realizing you have to do 100 more
thats a grind, and something only pure (paid) artists might enjoy.
here a random example of an isometric scene made from simple geometric shapes and simple textures
You dont need to be an artist to create these shapes (or generate these textures), its more programming skill.http://pokepetter.deviantart.com/art/Isometric-Game-Concept-181300309
here an example of very low res tiles with a very limited color palette:
a simple drawing, vectorized using inkscape:
this is a good example of creating a nice scene based on your technical skill (without the need to be a big artist)