I think that is why I am looking for a good lawyer, and architect before I EVEN think about paying up any deposits. Seems like between the two agents, it's a lot of yes and then no.
I'd forget the architect for the moment and focus on getting a good solicitor/abogado who knows what they're doing. If you can't build on the land, an architect won't be much use to you.
Your last sentence would start warning bells ringing in my ears right away. Lot of yes and no? Do not trust a single world estate agents tell you and be particularly wary of British ones—they're some of the worst out there.
At the end of the day estate agents are sales people —they sell real estate, that's how they make their money. In addition they should be representing the interests of their clients, in other words the real estate they're trying to sell. You're a potential buyer—they're not representing your interests.
If all that isn't bad enough, there's a lot of corruption in Spain to contend with—lots of back handers going on.
Tread very carefully indeed and pay and sign nothing until you're 200% sure that what you're buying has (or can be obtained) all the necessary permits you need to build and construct what you're planning.
It might also be worth looking for an independent Spanish/English translator to sit in on any meeting you might have through the process to give you an impartial translation of what is being said rather than relying 100% on your solicitor/estate agent to translate.