Can I have 'Other' as a topic?

It is possible to do so but we recommend that you do not create a topic labelled 'Other'. When in doubt, very often many authors will choose a topic entitled 'Other'. However, reviewers will generally not want to review submissions labelled 'Other': this creates a serious problem when allocating reviewers as there will be no reviewers for this topic i.e. you will end up with papers that the system cannot allocate to reviewers automatically. It may be better to ask authors to contact you if they feel that there should be an additional topic. 

If you will be re-assigning reviewers after the allocation, this is not as much of an issue as you can assign whichever reviewer you require to the submission manually.