why spend ten grand on a system if its not going to be done right and please consider the following:
detailing : get detailed drawings from your preferred contractor and discuss them here if yee like. this is the main problem imo with EWI. you have a few young lads banging it up and plasterer finishing it, very little consideration for the junctions at eaves, windows, ground, ventilation, fire breaks etc.
product guarantee: 'Sto' seem to be the only ones
materials: from an enviro prespective I'd go for the mineral wool or Cork ewi.
space issues: phenolic offers a good thermal value ratio to thickness, rockwool and eps are about the same, the Aerogel stuff is great in this regard as although its expensive it could be used where homes are on a footpath and space is an issue.
suitability: if you live in an old house (defined by if has ever been lime-washed) then EWI must be approached using breathable materials and preferably specialist advice
U-value: is 120mm enough? if it was a new house it might be 200mm or more.. but whats the point, if the thermal bridges are not dealt with when working out the details