Hi Lee
I appreciate I dont know your property or installation requirements, but unless you are running a business I personally dont see the need for 12 cameras?
I ran my own company in the UK for 4 years selling and installing covert and overt CCTV in business and domestic dwellings and from my experience very few people need so many cameras. However, I have a saying that what will do a lot will do a little!
The SWANN equipment is very good kit equipment. My only concern with kits is that they typically come with pre-connected ends (Such as BNC, RJ45 and Phono connections) which mean two things. Firstly, you cannot cut the cables unless you have the tools to remake off the ends, so you have to hide the excess cable somewhere. Secondly, the hole size requirement for a BNC connector is much larger than for just a coax or RG59 Cable, even bigger than the combined RG59 and power cable too.
I now recommend that DIY installers used a wireless system. I hated them in the early days but with advances in technology, I actually think something like the NEST, RING or BLINK are actually very good when you have a stable WiFi connection.
I have not procured any CCTV in Spain as yet, had no need, but when I do I will likely purchase from a UK based supplier (long relation and trusted) which actually goes against my other principle of trying to keep it local, but needs must in some cases.
In my (little) experience of fleabay, I think most people ship to most locations, its just a matter of delivery cost. I dont know how you are coming over to Spain but you will have another big box to carry if you have it delivered to UK, not an issue if you are driving or hiring a van etc
There are many advantages to the kit form you are suggesting, just be aware that the installation may take a little longer than you expect and you will need to purchase some install tools if you do end up doing it yourself, BUT, it is not difficult to do!
In simple steps: Decide on your camera locations, what you want to cover
Think about light levels, low light areas? Typically B&W works better than Colour in low light, despite claims! I personally prefer to have security lighting to give a well-lit solution for any camera to work! Intruders dont like light!!!
Locate a suitable place for your main equipment. Does it need to connect to your router?
Think about your cable routes
Think about safe access and working to install cables. Think about other services near your installation (electricity, plumbing)
Think about the aesthetics - hidden cable requirements or redecorating need
Give yourself time, dont rush
Very often Google and YouTube will be your friend!
As for the equipment itself, do your research and read reviews. Take some with a pinch of salt of course, you will always find some disgruntled customers!
Hope all that helps. If you need any further advice then please let me know, happy to help.