I used Liffey Architects for the design of my extension and I have to say the lad Barry Kane's idea was WAY better than the design my sisters friend of a friend came up with and I got Liffey down to a much better price, and he also drew up plans for a bigger alternative in case I might go for it even though I indicated it was unlikely - thought that was a good touch - all I gotta do know is get confirmation that my planning application has been granted in a few weeks and I'll complete the glowing reference.
I'm in a similar situation - bought a place in D12 and am TOTALLY gutting it. Doing a lot myself and due to recommendation from my sister on the job they did on her extension I'm using Sheerin Construction (087 6810427) for the bits that are too much for me (a lot!) and have found they show up when they say they will, clearly outline what I can and cant afford, do a good neat job and clean up after themselves so I'm well happy so far.
Oh yeh - some words of advice: check for asbestos and also lead pipes asap. estimate how long you think it will take and add 33% to it. estimate how much you think it will cost and add a similar amount. even with experience theres lots of delays and surprises that just cant be anticipated when dealing with an old house. if you are a bit clued in think about hiring tradesmen directly (especially if you know any) as this should save a good bit, but unless you know a good bit it may be best to go with a turnkey provider cos those property shows on TV sometimes make it look a lot easier than it is so you may be better off paying for the convenience. Oh and get 3 quotes for everything and good luck!