Now I am open to correction on this as things may have changed but I would have thought rather than help your case it would hinder it to tell them you are trying to set up a business. To get JA/JB you need to be available for and seeking full time work.
If you have been working I am assuming it is Jobseekers Benefit you are applying for and not Jobseekers Allowance?
If that is correct then I would wait until the benefit is up and running then apply for the Short Term Enterprise Allowance
http://www.welfare.ie/en/Pages/Short-Term-Enterprise-Allowance.aspx which basically is just changing the name of the benefit for the time it is payable and allows you work on your new business.
However it does say that it is for people who have lost their jobs, you might want to be careful around the terminology you use regarding losing/leaving the job
I'd imagine the reason you left the job could be important, if you let just because you are starting your own business then I'd be inclined to think you would be entitled to neither JB or STEA as you are not seeking work initially to qualify for the JB which you have to have to convert to STEA.
Now if you left your job because you couldn't hack the stress anymore and are now looking for work but don't find anything within the next 9 weeks or after that might be different, and you might have no option but to consider self employment in due course