We have experience with 2 different gas plumbers who recently did and are still doing jobs in our house in Dublin 5. One did a decent enough and affordable job (fitting high efficiency condensing boiler and 1 new rad) though the rad has the wrong output, though my partner told him to get the same size so he thinks that it is his own fault. I slightly disagree.
We will have another more affor gas plumber in this month to do a huge job (replacing microbore piping so all floor boards up, new rads and immersion heater and some other bits and pieces, quoted labour costs 1800 which is good value I believe)
I would advise you not to buy everything yourself unless you have an account indeed.
I don't have their contact details now by hand, but if you want I can PM you once they are finished in our house and then I have more experience with them as well.