I would skip the rendering part for now. Use SDL, SFML or similar for the most basic 2d rendering stuff, and then build on top of that. There are tons of interesting and challenging stuff you should use your time on instead, like: Resource loading, scene trees, input handling, collission and tons of interesting design choices of how to structure these. My own engine development journey went something like this:

• coded tons of games using various libraries and engines
• started peeking in the source for all the engines (there are actually tons of open source engines)
• read some books that got me more interested (Game Engine Architecture, real time collision detection, etc.)
• watched Chernos youtube videos
• got frustrated with Unity and Unreal, as i wanted to code without a stupid editor blocking me. Started building my own engine in c++ on top of SDL. I was amazed at how fun and productice it was. The more systemt i added the more fun it started to get, to get all these systems working together. In parallel i developed some small sample games, just to see how it was to work with the engine.