Freeview is the name of the (BBC-backed) digital TV system that uses hilltop transmitters to rooftop aerials. It is run separately from the "Sky" satellite-to-dish service.
free-to-VIEW is a term for satellitechannels that need a viewing card to watch, but not to collect a subscription. free-to-AIR channels are ones that can be received without needing a viewing card or subscription.
The free-to-AIR satelite service backed by the BBC and ITV is called Freesat. The free-to-VIEW service operated by Sky is called fSfS or Freesat from Sky.
As long as you have finished your first year, you can leave Sky when you want.
To do this just give Sky a call and tell them you don't want to subscribe any more.
You will still need to keep your Sky viewing card. If you stop subscribing on a Sky contract, you can keep using that card to watch 5USA, 5* and PICK TV, the so-called "free-to-view" channels. (All ITV channels are free-to-air).
It is not possible to plug an aerial into a Sky Digibox to receive Freeview channels because the boxes have not been designed this way.
You will continue to get the full Sky EPG listings; you just will not be able to watch subscription channels.
No! Sky does not use an aerial, instead it uses a dish and LNB combination to receive signals from a set of satellites in geo-stationary orbit on the Equator above East Africa. Normal Freeview recpetion requires the use of an aerial of a Yagi or log-periodic design aimed at your preferred transmitter. 'Preferred' here meaning the one that gives the best reception.
If you enter your full post code into this website you will be shown listings of available transmitters and which direction to have your new aerial aimed for best reception.