Hi Joanne,
1. If you don't have the money you need for Revenue then when the time comes contact them and ask them to give your a repayment schedule, basically you'll pay them in installments over an 18 months to 2 year period. You should expect to repay them somewhere in the region of €400 p/m which will seriously eat into your disposable cash.
2. Getting rid of the car is probably a good idea, if you can afford to be without it.
3. Stop contributing to your SSIA, or cut right back, you can't afford savings right now.
4. If you have equity in your house it might be worth considering a consolodation loan in this situation. I wouldn't normally consider it, but if there's no other way to meet the repayments and still have enough each month to live on then you should look at it.
-Rd