Tensioner failure on fiesta 1.6 tdci

Had car for 17months, took it back to garage through the first 12 months - engine light
on, they said malfunction and fixed, oil leak persistent, they did goodwill service and said
they couldn't find anything, coolant level dropping and required regular top up, they said
couldn't find anything wrong and topped it up. coolant continued to require regular top up,
then heard pop and car stopped. recovered to same garage after £500 of repairs they
said tensioner clip pulley? Had failed , causing cam belt to fail, put it back together ,
knocking noise, they took head off to find the valves had contact and car required new
head. BIll now stands at £1900 to get back on the road.
1) Is the cam belt and tensner pulley the one and same or 2 different parts?
2) Could the dropping coolant have effected the cam/tensioner causing wear which
contributed to it failing?
3)is it worth having a new head for the age and mileage of the car or shoul I scrap it and
not put good money after bad? it's year is 2007 and it's done 45,ooo miles
4) CAn I rely on this car if all repairs are carried out or is it the start of ongoing
maintenance problems?
all advice gratefully received.