Hey, the best and easiest approach for 3d models would be using daz3d as it has superior graphics, models and lots of assets you can use. For tiles, I brought them from steam, they're simply called "medieval tiles", there are multiple packs like "Medieval: Interiors", but you have to use photoshop to fully utilize them. I upscaled the tiles to 2x of their original size and make a lot of changes during mapping. What I do is called parallax mapping. I make maps with two layers, bottom and on top of that, I make another layer for lightning effects etc. The upscale software I use is waifu2x caffe edition. For compressing images which lets me reduce the size of the images (which I have not used for the demo yet) is "FileOptimizer". After compressing some of the maps are 2x smaller size without any noticeable quality loss. I've been using photoshop a lot and learning batching feature is a must to reduce the time it would take to edit images manually.
The program I use for game-making is RPGM MV. With some javascript knowledge, it's easy to make your own stuff for your game or just use/edit existing plugins which are offered for free by the great community RPGM engine has.
The best approach would just start making your own game. Most likely if it's your first time, you'll be redoing it after gaining some knowledge as I did, I scratched my prototype and made the game you see now.
If you have any specific questions, let me know!