Regarding the KNIME Community Hub spaces in Space/KNIME Explorer, you can view your spaces and the spaces to which you have read and write access permission. e.g. when a space owner gives you access to their public space. Currently, the drag and drop form Hub to Modern UI is not possible but I added your feedback to our list. For now, you can first download and then import workflow groups/components (.knar) in Modern UI.
Yes, we have it in our list and I added your feedback as well.