Prioritise and prioritise properly, divide up NEED and WANT. For every purchase ask yourself, do I
need this or is this a want. A brand spanking new corner sofa is a want, a need is something for yourselves and any visitors to sit on. A solid oak table with six matching chairs is a want, what you need is something to serve meals on. A shiny new bathroom set and full tiling is a want, a need is a functional toilet, a wash basin and either a bath or a shower. If it is a second hand house, use whatever is already there unless it is actually broken and non-functional, a 30 year old avocado-green suite that is still working will continue working for another year and won't cost you dearly when you are tight for cash, you can change it later when you have settled into a more stable spending pattern.
The one thing I would absolutely advise spending good money on now is a decent mattress. Bad mattress = poor quality sleep and given you will always spend at least a quarter of your time in your bed (and that is short-changing yourself, 6 hours sleep is too little) it is the one thing that I would not stint on.
In fact the cheaper and more second hand you go at first for most things the better. In a year's time, all things being equal, you will be in a better position to afford to do up a room with new furniture to your own taste, you will be able to buy at a less frenzied pace.
terrysgirl33 mentioned jumbletown.ie - definitely worth looking at - you never know what you might pick up for the bargain basement price of €0 and the effort of picking it up yourself.
Another one to check out is
freecycle
(an international freecycle website though it isn't as big in Ireland as other places because jumbletown had already cornered the freecycle market)
Also check out
www.donedeal.ie - not free cycle but you'd be amazed at some of the things that people don't need and want to sell.
Basically price everything and price it again, bargain hard and ask yourself - do you actually need it or do you just want it. Enjoy!