Top-up benefits are fine. She will need to be employed or self-employed after the initial three months for you to be able to stay in Ireland.
The biggest issue could be the Habitual Residency Condition (HRC) which is applied to many benefits. Basically it is very difficult to get benefits unless you are viewed as to have given up your life abroad to live in Ireland. As part of the test you will be asked about the location of your family, where your money is banked and clubs and societies you belong to to see where your "centre of interest is".
http://www.citizensinformation.ie/en/so ... eland.html
http://www.welfare.ie/en/Pages/Habitual ... Offic.aspx
If you have children and you or your wife are employed (not self-employed) for more than 19 years a week you can claim "Family Income Support"
http://www.citizensinformation.ie/en/so ... ement.html . There is no HRC for this benefit.
If she plans to be self-employed she may be able to claim JSA as an underemployed person if she passes the HRC (it is easier to pass if she is from the UK (Common Travel Area) and if partially employed/self-employed). If she passes the HRC they may make declare your means to be a few Euro a week and allow you to pocket the extra until it is reviewed again after several months. It can take several months (with arrears) to receive the dole though. There is also a provision for job seekers to get benefits transferred from one EU country to another but this would be at the lower UK rate of around £110 per week as a couple rather than the Irish rate of around €310.
It may take six months to get Rent Allowance and then you can only get it if your income drops for a reason outside of your control. If though you get assessed by the council you may get it sooner but many councils will not accept your application until you get your Stamp 4 (5 year residence card).
http://www.citizensinformation.ie/en/so ... ement.html
You may find some of the issues discussed here of interest.
http://www.immigrationboards.com/viewtopic.php?p=730423
