Moving goods from one country to another

Sometimes we need to buy goods in an European country (France for example) to sell it to the export from Belgium. We are VAT registered in both countries.
I’m wondering what are the good ways to declare (and pay VAT) when this is happening. Can you please tell me if the following cases are correct ?

If we buy the goods on our UK VAT number, I suppose we should move it (VAT speaking) to the country from which they will be exported outside Europe, so to our BE VAT number ?
How should it be done ?
Can we declare a triangular operation (FR supplier, UK us, BE customer = us again) ? With selling price to the BE number = the buying price on our FR number ?

Now, as we are not always sure where we will sell the material, we could have bought it on our FR number (then we would have paid FR VAT) in case we’ll sell it to french market.
But… we’re going to export it outside EU thru Belgium again…
So, this time we should declare an expedition from France to Belgium, “selling” the material to our BE number at the buying price, permitting us to get back the FR VAT paid to our supplier.