What's the best thing to learn if I want to write scripts to handle videos?

I often find myself needing to perform simple actions on large amounts of videos. I've used ffmpeg with batch files, but that's rather limited -- I need something more. I'm just not sure what. Do I learn to write AVIsynth scripts? Something more involved, like Python, incorporating ffmpeg? No idea. I'd appreciate it if someone could give me some tips as to what to study/look into.

For examples, here are some tasks I've needed to do;

- Assess every file within a folder (4,500 video files). If the resolution is 1 megapixel or greater, move to "Large" subfolder. If it's less, move to "Small" subfolder.
- Assess every file within a folder, and if its audio bitrate is over 192 Kbit, transcode it using LAME.
- Assess every file within a folder, and if its video bitrate is over 3 Mbit, transcode it using x264.
- Take 8 screenshots from even intervals within each video, and write the filename of that video into the image as a text overlay; ideally, put these 8 screenshots together in a grid and save as one low-quality JPEG file rather than 8 separate ones.
- Transcode all 1280x720 videos within a folder to a specific setting (say, DNxHD 80) and all 1920x1080 videos within a folder to a different setting (DNxHD 36).
- Transcode all videos that are currently MPEG-2.

And so on and so on, you get the idea. Not terribly complex things, but things beyond the reach of a batch file.

What's my best course of action here?