If I were you I would fill out the form to the best of my knowledge and also ask INIS for advice on specific questions.
You can also try making an appointment with the Immigrant Council of Ireland, it's a Non-Profit organisation and they give free advice to immigrants.
http://www.immigrantcouncil.ie/
You can also talk to the Migrant Rights Centre Ireland (another non profit organisation):
http://www.mrci.ie/
For the reckoning of your residence INIS will consider that you have lived in Ireland continuously for 1 year before you submit your application (so when you submit your application you must have been living and working in Ireland for 1 year). Then, they will look back at the previous 8 years and they will count the number of years that you were living and working in Ireland. The total number of years that you must have been living and working in Ireland must total 5. Details are described here:
http://www.inis.gov.ie/en/INIS/Informat ... 070409.pdf
From my understanding, this would be a valid scenario:
You apply on 20th October 2009 and you have been living and working in Ireland since the 20th October 2008 - this counts as 1 year.
From 20th October 2004 to 19th October 2008 you were studying. - This time will not be couned towards your naturalisation
From the 20th October 2000 to the 19th October 2004 you were working and living in Ireland - This time (4 years) will be counted towards your naturalisation.
In total, you would have lived 5 years in Ireland, so you qualify for naturalisation.
Now, this is my interpretation. I would recommend asking INIS and the Immigration Council/MRCI as well.
I don't think they would consider the time you were married since you're now divorced. But I'm not sure. Just remember that with your application you will have to submit copies of your marriage certificate and divorce certificate.
You could also make an appointment with a solicitor. But as tiggs said, applying through a solicitor will not make your application any faster and it will be more expensive. But maybe a chat will not be that expensive (you just pay for 1 hour of the solicitor's time).
Please note that your signature of the naturalisation form has to be witnessed by a solicitor (which will charge you around 10 euro for that). You could ask the solicitor at that moment these questions and whether he considers you fulfil the statutory residency requirements.
As for timelines, the INIS website claims that naturalisations are now taking 24 months to be processed. However, most of us have experienced delays of more than 36 months, as we applied before the Naturalisation Section was decentralised to Tipperary. Hopefully, you will get a decision within 24 months.
Good luck!
LP