Well...post some code up when you can. daves advice the best. Chunk this project up. You can spend more time on sensors, wiring and libraries than getting the big picture logic to work.
Also...many a ways to work with infinite loop. A lot of my stuff is timing based. Also..a lot of my stuff doesn't need to be checked/done 10 times a second. We can help you there, just post up your first attempt.
Maybe the watering logic using "dummy" sensors and serial print outputs.