Ok. Keeping goats is perfectly normal. Don't let anyone tell you any different.
One goat would produce enough milk for 2-3 of you and you would be able to make cheese. My girl is producing just over four pints a day which is more than enough for the two of us. I make yoghurt and soft cheese. to make hard cheese you need somewhere cool (not the fridge) to keep it while it matures. I lost loads the one year I tried it because I couldn't keep it at the right temperature. Having said one goat is enough, goats don't like living alone and would be far happier to have goatie company. Also the yield goes down each year so, by having two, you can breed from each one alternate years and keep the yield up. You would need to check the regulations in Spain but here you are not allowed to sell milk or cheese or yoghurt unless you are a proper checked supplier, unless it is marked 'Not for human consumption' although what people then do with it is up to them.
Which brings me to yes, you usually have to breed from them to get the milk. Having said that, Plumseverywhere on here has a maiden milker, one who has never been mated but who still produces lots of mik every year, but this is unusual. What happens to the kids is up to you. Some people take them away from their mothers at birth and either bottle feed them or, if they are male, kill them. Personally I prefer to leave the kids with mum and take some milk for us. There isn't a lot spare which is another advantage of having two producing milk. Once they are weaned, you have the option of keeping them, selling them or eating them. That is not easy. The last one I bred was male and I named him Curry so there was no doubt in my mind where he was going to end up. It still took me a long time to actually send him off for slaughter and I think that the fact that someone else offered to take him when she took hers made it a bit easier. He does taste good though.
If you raise a male, he either has to be castrated, soon after birth usually, or kept well away from the females. If kept entire, he will stink so well away from the house is also prefereable.
The usual, as I said, is to breed from each alternate years but mine last one and the current milker, her daughter, produce so well that I leave it longer. It's two years since Pom had Curry and she still produces enough. Flo was still being milked four years after giving birth to Pom. Cloud, my younger one, who I bought from a dairy farm, is now 16 months old so I will be looking to get her in kid this autumn so she will give birth when she is two.
In the UK goats come into season every three weeks from September/October time through to February. This may be different in warmer countries. Pregnancy lasts 150 days.