You can't download series information with the Goodreads Sync plugin. However you can with the Goodreads metadata plugin, which works the same ways as the plugins that come with calibre such as Amazon, Google etc. You can also import series information if you exported from Goodreads to CSV using the Import List plugin.
I don't know what you mean by "top 10 genres". The Goodreads Sync plugin is about synchronising to your shelves, not anyone else's. You can choose from your list of shelves which ones you want to synchronise with. It just so happens that a subset of Goodreads users happen to create shelves that represent genres, and this plugin supports that, however it is not a requirement.
As for throttling limitations, theducks has covered it. Goodreads have some very strict terms of service on their API, and to make sure one or a few users didn't get everyone banned I put that limit in place. If you are doing bulk operations with goodreads there are other ways to do them - specifically using their import/export via CSV files. You can both export from calibre using the catalog feature, and import to calibre using the Import List plugin. On an ongoing basis of syncing books it shouldn't be the case of the threshold being an issue, it is only for some first time users depending on how you are using this plugin and whether your books are already on goodreads shelves.
BTW please don't double post your questions - once on the Goodreads Sync thread would have been enough. Now I either have to repeat my answers, or leave your post unanswered which confuses future readers of the other thread.