If I plug USB hub into the raspberry pi will it drain much more power?
Will my raspberry pi run slower?
Depends on what you plug into the hub and whether or not the Hub is powered or passive (ie. does it also plug into an AC source for it's own power.
A hub by itself will only use a very little amount of power but if you plug in several usb devices into that hub that use the usb port to get their power then the usage starts to add up !
A hub will not make any change to how the pi runs as far as speed goes but if you place too many devices that are all using power and it gets to a point that there is not enough power available for all of them the pi may begin to shut down randomly as it lacks the power to run. (which is why having a good ac outlet device becomes more important as you add more devices that get their power from the USB bus)