The default grid layout content editor seems to be part of the rich text editor. this allows to embed videos, but requires the user to enter the dimensions of the video (and rely on content editors to set a video size). I have created a document type that simply loads a responsive video (video url only real parameter) but I can't find how I would integrate the document type here, and I assume I can't. So what is the next option? Is there a way to include a "grid" system based on bootstrap but then have the individual columns have their own independant content / document types? (so left size I can include a document type for the video and on the right column have a rich text editor)?

Umbraco has a few different property editors for building layout based content. Are you using the Grid layout property editor? This isn't based on document types, and it's also obsolete, and IIRC it won't be part of Umbraco 13. But Umbraco also has the Block List and Block Grid. The latter works somewhat similar to Grid layout, but it's based on document types instead, which makes it so much easier to configure custom elements/blocks.

Embeds outside of the rte.. https://github.com/dawoe/OEmbed-Picker-Property-Editor