List of problems with my saph cosworth

Pulls slowly and lumpily in low gears (not too bad once warmed up)
low oil pressure
loosing water
Turbo seems to get very hot

I think it might be my head gasket? Is it OK to drive until I get it repaired or will I do more damage? If it is a head gasket what kind of cost am I looking at for replacement? And finally if the head gasket is damaged / leaking is it likely to have done some damage to the engine also?

Would appreciate any advice by the on the above., thanks in advance