Moses2013

Although one has to note the OP is looking at Estepona area. Nights down there are a lot milder, but during winter it's also more damp than Valencia in general (microclimates aside).
Even where we are near Lloret it's a lot drier than Estepona during winter and they see double or triple the rainfall but our nights are a lot colder and we see slightly more rain in summer.
Winter:

Summer

Millhouse

I'm currently building a large house in Marbella and have an excellent developer working with me. If you want to discuss more reach out. To answer your questions:

1/ Lawyers are useless - they are not liable for their advice and it is often wrong. You need a solid Architect for this to check the planning / zoning rules etc.
2/ Your plot most likely does not have the permissions you are being told it has
3/ Company vs Personal. Largely makes no difference - while you think you will skip the capital gains tax, the company structure is looked through here and any attempt to avoid capital gains tax is a huge issue.
4/ You will need either "the big license" or a self declaration. Either way, you will need an Architect to sign everything off. He puts his name to this and my experience won't break the law/zoning regulations.
5/ Don't be an idiot on how you build... respect noise, days of the week etc. One phone call to the townhall and your site will be stopped. I know people who attempted 12 hour days 7 days a week. It ended badly.

Moses2013

I don't totally disagree, but would be careful saying this. An architect doesn't check disputes, access rights and can't deal with missing IBI payments, won't get you NIE numbers and help with the buying process (bank account etc.). The architect is also constrained by the findings of the geotechnical survey.

Before buying do plenty of research.
When buying, use a lawyer and do the geotechnical survey.
The geotechnical survey will actually show if the land is even suitable to build. In this case the land must already have one if there is really planning permission. I would also request to see this before paying anyone. Then you will need the architect.......

Millhouse

Yes to be clear, we had a lawyer, technical engineer do a site survey and the architect.

The lawyer found issues with previous build issues. Most of his findings were not totally correct, but he did check for previous disputes, payments etc. He did flag a build up area issue with the site.

The engineer highlighted the built up area issue, and some issues with drains and trees. The laywer told me about the trees.

The architect found the correct planning documents and solved the BUA issue.

The developer would only develop around 90% of the project until the architect solved the issue. The developer presented the project etc. to the town hall.

You need all. My point on the legal is unlike the UK, they are not the end of the process nor can be fully relied upon. All that said, I was very happy with mine.

Moses2013

Good points and hope you can enjoy your new home soon enough. Would still be interesting to know if the land the OP is planning to buy really has planning permission (a project) or not. Often people disappear and you never know the end of the story.

Millhouse

The only thing I can be assure of is that the site doesn't have the planning permission he thinks it has

Millhouse

I have put 10KW of solar across mine. It should be enough heat (use heat pump & underfloor) and cool the home.

Jono2000

Thanks, good advice I think.