Hi Craig, To answer your questions -
Stamp Duty: In Spain you will pay IVA (VAT) for a new property or a transfer tax for a 2nd hand one - this will be in the range of 6 - 7% depending upon the region of Spain you buy in. The percentage is based on the declared value stated in your escritura (title deeds) which may be less than the actual buying price.
Also there is a Land Registry tax - again this can vary upon area and also whether it is registered as a main residence or a 2nd home (holiday home) Maximum should be around 1 - 1,5%
Regarding your other point I assume you are talking around ensuring that the property/land is registered into your name. If you buy a fully legal property (take legal advice or another option is take a mortgage - banks wont loan on illegal property) then you wont have a problem.
Ok ?