Hi,
Thank you for your questions.
1. You cannot use Edge Delivery blocks & sections outside of Edge Delivery pages. You need to move the whole page on Edge Delivery. There is not need to move your whole site, you can start moving just a few pages and delivery then in a side-by-side fashion using CDN rules.
2. As of today, you cannot use Universal Editor on top of Sharepoint or Google documents. We have not seen (yet) real demand of authors to do both on the same page. It will add authoring complexity we want to avoid with doc-based authoring. However, if authors want to switch at one point, we have tools to help moving the content from doc-based to AEM or the other way around.
3. For Sharepoint / Gdrive documents, this would be handled by the respective solution. For Universal Editor, collaborative editing it is on the roadmap for 2025.
4. Yes, that is possible, but keep the authoring experience in mind if you need to cross-reference between content sources.