Can I use two USB together? I.e., USB of wireless WiFi and USB of wireless mouse/key board. WiFi is 802.11n NIC and mouse/keyboard 2.4G
USB Wireless LAN (802.11) is 2.4Ghz or 5 GHz. Mouse & keyboard are using the Bluetooth (BT) protocol (NOT 802.11). BT is also 2.4GHz, but not exactly the same the range. You can switch bands for WiFi if needed, but they do not interfere under normal usage. Having that said, not all radio devices are perfect and many (hunderds) if BT devices can pollure WiFi range - this will not happen for home usage.