My series of questions:
Can I boot a computer over my network (turn it on)
Yup, if both your networkcard and motherboard support it. Google for Wake-On-Lan.
Configure your BIOS to wake on lan, then use a program like
WakeOnLan
Can I send it a command to start scar and RS to start autoing?
Not directly, but you can run a server to listen for commands, or use remote control (see below)
Can I make it stop the script and shut down at a certain time?
Yes, but you need to modify SRL a bit. Just do something in FindNormalRandoms like if (TimesUp) then terminatescript;
So is there anyway to take over control of computers just from my Main computer?
VNC, I use UltraVNC myself, but you can use TinyVNC or RealVNC too.