1. Make sure you have a target market - most crucial point. A good saying is 'if you try to sell to everyone you will sell to no one'. Pick your niche, if you can make really good plants/trees then triple down and make lots of these and you should see some sales, for example.
2. 3dsmax/maya both offer indie licenses quite cheap at around $300 per year depending where you are from. Again look at point 1, if your target market is hobby 3d artists then blender is a good choice, if you want to target professionals in the industry then make sure your models are ready in max/maya as well.
3. You will need to model things that are difficult/time consuming to build. For example, if it takes the buyer 2+ days to build that object - lets call it a photo realistic sofa with stitching, fabric folds, high quality textures and materials, works well in a variety of lighting then buying that sofa for $50 is a bargain because most pro's charge their time around $50 per hour, so that's a good trade for them.
4. Your models are mostly concept items and some of those can be made within a couple of hours with enough experience. I mean this in the most sincere way I only have good intentions as you asked for guidance. I would have a tough time modelling that car you made recently to be honest, but if its not in demand from a client then its probably going to be difficult to sell. For example when the Monteria plant was requested by every single archviz studio 3 years in a row, if you were selling a high quality version then you probably seen good returns on your efforts.
Some things to chew on.
