You should be fine.
Most builders/ sellers ask for a 10% deposit, and most banks offer 92% mortgages. Most sellers are so desperate to sell they will have no problem accepting an 8% deposit, makes no difference to them in the end as they still get 100% at the end. You will need to get your solicitor to put it in writing that you are only willing to pay an 8% deposit (but that you will work fast, so they will get the full amount really soon afterwards). This is what I did and had no problems with it.
With regard to the €5k booking fee, this will be deducted from the €23k deposit, so that when you do pay the 8% deposit you have agreed, you are actually only paying €28k. Does that make sense?
Your questions aren't stupid. I had all the same ones six months ago!!
Don't mind people who say it's not possible, if you want it, it will be!! While it will be tight, you'll make the legal fees and survey! just don't expect to be able to afford luxury furniture when you move in. I had no money left after my deposit and I did it...here's how...
Ask your bank for a 3 month moratorium (or deferred payment option). Most of them do it but you have to ask. This is when you don't start making repayments til 3 months after you've moved in. That way you pay all your legal bills, etc off your salary this month, and then just be prepared to live off your credit card. You'll have it all sorted (and a few bits of furniture) by the time your first mortgage repayment is taken. Happy Days