Not the cheapest solution but for the composite and s-video stuff you might have this is what I'm using with my setup...

I do have my retro consoles modded with composite/s-video as needed.

I have those systems plugged into one of these:

https://www.extron.com/product/system7sc

Got mine loose for about $45 shipped from shopgoodwill over the summer. Bought the remote for it for another $15 shipped from ebay.

Everything that plugs into that Extron is then upscaled and ouput at VGA or RGBHV. So I use a short VGA cable from it to my OSSC and then HDMI out to my TV. You can set the Extron to output at various resolutions both 4:3 and 16:9. Then using the OSSC I can create profiles to save to it to dial in the systems more as needed.