If you have already published articles based on the content of your thesis, you should check that you will not be breaking the terms of publication contract by making the thesis freely available online. If you have not already, but intend to publish all or parts of your thesis as a book or journal articles, please check the appropriate publisher’s policies on pre- and post-publication, as these vary and may specifically ask for the work not to have been made available in the public domain prior to publication. In the case of journal articles, it should be possible to publish material from your thesis if it is sufficiently further developed. Journal editors and/or publishers should be able to give you advice on this. If you don't intend to publish any of your thesis elsewhere, or are sure that your publisher(s) has no objections to the thesis being made freely available, then you can opt to make your thesis open access immediately.
Making your thesis freely available on the Internet via ORA constitutes a form of publication which may make it more difficult for you to get your thesis published in other ways you might have anticipated, eg in the form of a book or journal articles. You may have to revise the work for publication in other forms more substantially than might otherwise have been necessary. Publishers differ in respect to their policies on this issue, so you may wish to check the appropriate publisher’s (if known) policy - and publishers are adapting quickly to an environment which is much more geared towards open access than in pervious years.
On the other hand, it may be some years before articles you submit now will be published, and you can’t be sure that you will get a book contract. In the meantime, your work will have little visibility. Additionally, publishers are increasingly reluctant to publish books of theses. It may be better to get your thesis out into the public domain, and set to work developing it further or in a more general context for publication – or moving on to a second major publication project. In the case of journal articles, it should still be possible to publish material from your thesis if it is sufficiently further developed; journal editors should be able to give you advice on this.