Need help with making up mind to adopt!?

Hello, I am a father of four beautiful children and married ten years to my wife.My wife lost her her sister due to a battle of cancer she only was diagnosed 8 months ago but sadly she lost the battle and its really made my wife downtrying to cheer her up these days is hard as they grew up together .she left behind a beautiful baby boy who is only a year and a half we found out her sister never decided who would take care of her child after because the death was so sudden .We are from ireland i myself am not irish in from the Netherlands and im dutch .i myself have no problem with taking in the child me and my wife love children and before this happened we were trying for our fifth child for over a year but have found it hard to conceive.I admit we are not perfect but i think we should keep him in the blood.we have good jobs im an accountant my wife's a nurse and i hope that way it will stand good for us so if we decide to we can get custody i think it will be up in court in about 3 to four weeks time im not 100% sure.I've not mentioned it yet with my wife but i am going to after i get advice.The child is with his Grandparents at he moment,his father is not in the picture as he didn't want to get involved when he was born.I think we can cope very well with this child as our oldest is nine down to age four so they too are fit to care and help this child when growing up .What i am wonder is would my nationality stand as im not irish but taking custody of an irish child? would we be too old to adopt im 43 my wife is 32? Could they tell us we have no room as we've a four bedroom house?And also how do we tell them we want to rared this child? i know my wife will want to because she would do anything to have something left with this child.Over all is this a good idea? Thank you very much for you're time,and im open to any advice