Can Arduino accept RS232?
It does have "regular" serial inputs & outpus. But they are not the correct voltage for RS-232, and RS-232 has a couple of handshaking lines. If you want to do it "right", you'll need to add another "little" chip. One such chip is the MAX232
Sometimes, the handshaking isn't used, and sometimes it "works" at 5V, even though that's not to spec. The handshaking can be done with a couple ofthe other digital inputs/outputs. Even if you can get-by without the special ship, you would have to somehow protect the Arduino from the (higher) RS-232 voltages, but that's no big deal.
There are lots of options & variables in the RS-232 protocol... It's a lot simpler for the programmer
than USB, but if the software doesn't automatically set-up the baud rate, stop-bits, and handshaking on both
ends, RS-232 can be more difficult than USB for the user
Can it store inputs and then make decisions based on these stored values?Yes!
It's very good at that! Computers (and microcontrollers) can "make decisions" by doing different things according to if-statements
along with logical AND & OR operators
Here in California there is a law requiring power companies to buy unused energy from people with solar panels. I know a couple of people with solar panels and their electric meter actually runs backwards when they are generating "excess" energy!!!