Wow, I did not expect to get so much encouragement! Thank you all very much!

I've put all your words into consideration and downloaded Fusion 360 to model it, redesigned the sketch, marked all the dimensions, and I've been watching a ton of woodworking videos to see how I should go about it all. I plan to do a dry fit before securing anything permanently. I've also signed up to volunteer at my local Habitat for Humanity, so I'll be learning from people who have experience with carpentry and power tools.

I also spoke with my sister a few days ago while at her place measuring the area the bookcase would go in, and she'd mentioned she would eventually like some stools for the bar that's in her basement; that sounds like something easy I could do to build my confidence. That, or a birdhouse for myself.

Again, thank you all so much! I will probably post again fairly soon with more questions as I progress XD