Goodmorning, I want to realize these sistems:
-automatic garden with humidity sensor, a photoresistor and a water pomp
-temperature rilevation with wifii connection, so I can register my data on a server
-movement and light rilevation for a street lamp
I'll do demostrative models, so I don't need nothing of too expensive or so professional.
What components should I buy? Any advice? Thanks and excuse me for my English but I'm Italian.
I suggest you investigate each of them separately. There will be plenty of Forum Threads about humidity sensors, LDRs, pumps and WiFi.
Write a short program to learn how to use each part on its own. Only try to combine them when you can get them all working separately. However when designing your individual programs keep in mind the need to combine them so (for example) use different I/O pins in each program. That way you won't have to re-assign pins when you bring the programs together.