If all of your clients are VAT registered and if you have a reasonable level of VATable costs then even if under the threshold ( €35,000 services and €70,000 sale of goods ) it may be worthwhile registering for VAT. You need to look at what costs you will have, if its a service then costs such as Light/Heat, Phone, stationery , etc. will all have VAT on them. If its sale of goods then your suppliers will most likely be charging you VAT on the goods. If you have done a projected P & L account for set-up purposes it's simble to run down this and extract what the VAT would be likely to be.
If youre clients are not VAT registered ( eg the general public mainly ) then registering for VAT while under the threshold may make your charges less competitive to other similar traders who have not registered for VAT