Hi Paula,  Any new installation would require commissioning whether it's a legal requirement or not here I'm unsure,
We brought a woodburner over from the UK with a back boiler attached to give us a little heat via radiators, with it being wood fuelled it does take a bit to get the temperatures up,  depends on the number obviously,  Steel or cast ?  depends on price really ours cost £650 in the UK not seen one here with the boiler, but the standard wood burners tend to be steel and cost wise from about 250 euros.
The flues in the UK have the joints "female up" that is so condensation does not run down the inside and wash out the jointing compound and only the terminal is the other way around. Here I remember it being reversed ..cannot remember now, but the off take from the boiler is usually female.
Material wise you can get anything if you're willing to pay, galvanised, enamelled or factory insulated stainless steel, again can be an expensive item, we brought ours over with the boiler from the UK and plumbed for the enamelled as it was inside the property to generate more heat.
Hope this helps