Generally, from what you have described, you could/should be able to carry out the proposed works without planning permission (as long as your house is not a protected structure or in an architectural conservation area), especially if the attic conversion will not be deemed 'habitable'. Generally, the provision of roof windows to the rear of a house are considered exempt from planning (and the staircase/converion itself should not require planning permisson).
You should seriously consider engaging an engineer and/or architect to advise you on planning matters, structural issues and building regulation compliance (even if you do intend to do most of the works yourself). There is a lot to consider! There is very useful information contained in this leaflet: http://www.environ.ie/en/DevelopmentHou ... 657,en.pdf
At the end of the day, if you decide to sell your house in the future (or even borrow money 'against' your house), you will need opinions on complaince with regard to both planning permission/exemption and building regulations, so, you should ensure, in the first place, that the works are compliant.
On a completely seperate matter from planning and building regulations, you now also need to consider Health and Safety. Have a look at this: http://gallery.mailchimp.com/956021ef7d ... _guide.pdf