Comprehensive guide to renting in Dublin?

Hi everyone!

My husband and I are moving to Dublin soon and I am frustrated at the lack of information around renting online.
I see the papers we will need, what I am not finding is how estate agents/realtors work and I'm not finding general renting advice.

How does it work? Does the tenant pay the estate agent or the landlord? How much? How soon in advance can one look? How does one know if an apartment is a dud or in a dodgy area?

What if the apartment has ugly furniture, may we replace it?

My husband's office will be right by Fitzwilliam Square. Does anyone know the name of that neighborhood? I know the one next to it Ranelagh and next to that Ballsbridge but I can't find which neighborhood Fitzwilliam square is in.

I would appreciate any answers. I have googled it and am somehow just not having luck!

Thank you in advance!