In the Edison module, when the pin mode is chosen as gpio, it can be programmed as an input or output. Inputs have programmable pullups or pulldowns. Pullup value can be 2, 20, or 50 kohm. I2C pins also have an additional 910 ohm value.
Yes, it is possible to attach for more than two devices to the SPI bus. In order to do this, the SPI devices need to be set to the same speed so that the communication does not fail.