A uk mobile would need to be unlocked and thenassigned to whatever Turkish network you decide to use, not a great hasstle but personaly, unless you want all the bels and whistles of a particular uk bought phone I would just buy a cheap basic phone here.
You need residency for a contract mobile, rates and plans vary as in the UK.
Yes.
You will either have to have residency or a neighbour who would be willing to share his wi-fi with you, or find a Turkish friend who is prepared to have a landline installed for you in his name.