Hi, I'm Ganapathy, I have rich experience in Arduino, GCC winAVR, Atmel studio, for Atmel Series microcontrollers, I also write programs for ARM-Cortex M Series, PIC32, PIC16F, PIC18F controller
Also I'm good at Analog and Digital design and Interfacing
I can create you class for this SSI interface so you can create maximum instances you can
since its a multidrop configuration so Hardware can be interfaced without any problem, you can methods to read each sensor
Regarding Solenoid driver you can use Relays or Discrete transistors which would be cost effective but take some space on PCB ,I can give the schematic for that if you want
For more information contact me
Thank you