1. I don't know about affecting your benefits, you need to talk to the Social Welfare officers. AFAIK all those back-to-education stuff is only available to long-term unemployed. I had the same situation as you a few years ago, and the Social Welfare office "closed" my claim, even though I had clearly and persistently indicated that it was a short-term contract. So the clock on my claim was reset to zero.
On the other had, I've got friends who did temporary work of a few weeks and were able to continue their benefits uninterrupted after. I really think it depends on the clerk in Social Welfare office.
2. Tax back - assuming you haven't worked in 2011, you will be able to ask the Revenue to issue your tax credits for the remaing 5 months of 2011. I simply can't remember the term for it. Just call up your local PAYE office and explain and they'll know what you mean.
You will probably pay very little in PAYE as you'll have unused tax credits. But PRSI/USC will probably still take a big chunk out of your pocket. The less you pay in Payroll, the less you'll pay in PRSI/USC, so you should maximise your expenses.
As an IT contractor, you need to maximise your expenses, so look up the Askaboutbusiness section for advice there. Legitimate expenses include a proportion of the rent for your home (you'll obviously set up one room as a home-office), a proportion of your energy bills, your mobile phone bill, your broadband bill, and your bus/luas/taxi fares. You are also entitled to award yourself one gift voucher for €250.
Just remember that it's still money that you could be saving, so don't go crazy and buy a new computer, bicycle or anything else like that.
As for tax credits, don't forget to apply for the Rent Relief (due to be abolised soon), medical fees etc.
Also, have you applied for a medical card while you are unemployed? If you hold a medical card - even of 1 day - you don't need to pay the Universal Social Charge, I believe.