Plumbing a new house - price

The labour price is very difficult to gauge - is there pipework in place for rads and/or are you redoing everything from scratch.

You seem to have the zone idea right but putting underfloor in the kitchen only. You need to do a search of the threads here and elsewhere about underfloor heating and the fact that you need the heating on all the time to maintain the heat. You then also have complicated control/mixing equipment to control/feed the underfloor as it does not need to be as hot as the water feeding the rads. It would make more sense if you wanted to go that way to underfloor heat all the day/living/bathroom areas and rad the bedrooms. Think of it this way you want heat in the kitchen, bathrooms and hallways in the morning. The boiler is firing all night to keep the kitchen at a comfortable level(setback) and then it comes on full blast in the morning to heat the rads - think of the oil you would be using.

With five bathrooms you should invest in a large min 300 litres steel glass lined cylinder which would be run as a pressurised system see www.rvr.ie for idea of prices.

Also
do you want showers (pumped or just standard pressure) in each ensuite?
what sort of quaility bathroom suites do you want prices range from €220 to €2200 and beyond?
Perhaps you should think of getting a dual coil cylinder and have the solid fuel heat some water for you.

The best way to approach this would be to sit down and write out what you want as a consumer ie loads of hot water, energy efficency, easy controls etc etc and then take it from there.