I need 70 or more input pins for the Arduino -how to do this?
The best way I know to do it is by using the MCP23017, which gives you 16 extra GPIOs via I²C communication. They can be configured for both input and/or output. I've done it myself and it worked like a charm. It has 3 pins for dynamic addressing (3 bits), which allows you to use up to 8 (0..7) MCP23017 for a total of 128 extra GPIOs. 
This is the chip datasheet:
(http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf)
There's a lot of examples about its use on the internet. Just google for "MCP23017 arduino" and you'll find them. For example:
http://tronixstuff.com/2011/08/26/tutorial-maximising-your-arduinos-io-ports/