The tax break for pick ups is the road tax, not the purchasing tax. They're considered to be used for agricultural work and the two door, or 'cab' versions are taxed less than the four door versions. But to be honest the road tax isn't much anyway.
Getting a licence, if you already have a UK licence for instance, means you won't have to pass the Thai driving test, such as it is. You will still need to do some tests, like a multiple choice theory test and I believe a kind of a sight test which involves distance perception. You should contact your local Department of Land and Transport for their specific requirements but here's a link to the main page of their website (always check local requirements as they often vary).