I don't have a glo, but I presume the annotation functions are the same across all devices, though I could be wrong.
In terms of what you can do with a book, you can bookmark pages, and you can highlight parts of texts. You can add comments (notes) to these highlights. One negative point is that you cannot highlight text across a page: so if the paragraph you are interested in goes over the page, you'll have to reduce the font so that the whole bit that interests you fits in a single page, and then highlight. There may be better ways, but this is the only one I know.
Coming to your questions:
1. within a book you can call the list of annotations - if you have many, it will go over various screens. Once in the list of annotations, you can either jump to the corresponding page in the book, or you can simply read the text you have highlighted. If you have also annotated it, you will see your note on top. Even if you have several pages, it does not take long
2. I don't think you can see all the annotations in the book, as they are accessed from within each book; but again, I do not know for sure.
3. you can search for text in the book you are reading (I think this is a pretty basic function all e-readers have), but you cannot search specifically for annotations - I don't know of a reader that does.
4. sorry, no idea (I mean: other ereaders, including sony I think, as well as Onyx's M92 and Pocketbook 913 and 903, allow for free-hand annotation, something you cannot do on a Kobo. But if this is importanto for you, perhaps a tablet is better.
There are other things you can do on the Kobo with annotations, however. First of all, you can send them to Calibre (though if you are new to ebooks perhaps you don't know Calibre); secondly, you can use Tshering
"annotation extractor" (works on windows only). This is very nice, because it creates a txt file of your annotations - you could then create a larger file containing all of your annotations, perhaps separated by book, and put it on your device. So you could search your annotations there, it will be some sort of index file.
There is also a feature to create a catalogue of your books, linking to them, with Calibre - perhaps one could ask in the appropriate forum if any kind soul has thought about creating a plugin that extracts annotations from calibre (after one has sent them) and creates a book with them where they link back to the proper page in the original book.