Suitable components for logic control
From what I gather from the comments, you don't want to use a ready built and/or hobby type platform.

You are right, an R-Pi is way overkill for switching a few relays and reading some sensors, and for all it's processing power is not as useful as many small microcontrollers would be with e.g. ADC and other low level peripherals.

So I would advise:


If you have never worked with electronic components, don't assume the missing knowledge you need is "elementary" - if you want to avoid using a ready built platform, there are many things that can complicate even the simplest of electronics firmware/hardware tasks. So be prepared to spend some serious time reading and soldering.
Grab a small microcontroller like a PIC or AVR, a breadboard, some basic components (see e.g. Adafruit or Sparkfun for starter component kits) and start there (for a proper selection see Mouser, Farnell, Digikey, etc).
There is lots of info out there to get you started, just head over to Microchip or Atmel and take a look at the starter kits (an example is the 8-bit based PICkit3 starter kit, or a more powerful 32-bit option is the PIC32 starter kit). There are plenty of App notes and tutorials on the sites mentioned above.
You will almost certainly have to learn some C, it is the main language for small to medium microcontrollers. There are more exotic options like graphic driven firmware design using flowcharts and such, or C++ for more powerful micros like the ARM Cortex, so if you really want to avoid C have a look around for alternatives, but it is likely to make things more difficult for you.  
Grab a basic electronics book - Practical Electronics For Inventors is a great introduction to all the components and basic theory. It does not really cover the firmware side of things though, for that have a look through options on Amazon, Programming 32-bit Microcontrollers in C is a good one if you go for the PIC32 starter kit.
Lastly, jump right in and come back here when you get stuck. It's easier for us to help you with specific problems as they turn up, right now you just need to get going with something (anything) and find your feet as you go along.