Insurance - I do not know your father's circumstances so I cannot comment. I can insure a 2.8 Capri for about £200 fully comprehensive.
Tax - £190 a year (going up again soon I think)
Fuel - Anywhere between 20 and 35mpg really, depending on engine choice and how heavy your right foot is.
Tyres - £35 to £50 a corner.
General service parts, suspension consumables - no more or less than any other generic 80s/90s Ford.
The Capri was never an inherently unreliable car, there isn't a huge amount to go wrong with it really. They are very easy to maintain at home on the driveway or in your garage. What you need to be aware of is that the components will be older and more prone to failure than those on a younger car. This is counterbalanced by the low cost and simplicity of rectifying these issues when parts fail.
What is expensive is repairing the structure of the car and keeping it in good condition. This summer I need to put the Manta on axle stands, strip back the floor to bare metal, inject the cavities with Dinitrol/Dynax wax, and then repaint it entirely with chassis paint followed by a layer of Stonechip, followed by a layer of underseal. It will take me about a weekend or so to do this at an enjoyable pace., depending on drying times.
I dread to think what the cost of such work would be at any sort of garage, even though it isn't "difficult" work.
If your dad is not prepared to get his hands dirty then yes, a classic car of any sort will cost a lot to run because you'll have it in the local garage every time the lighting earths get corroded or it develops a misfire from a blocked fuel filter or dodgy rotor arm. If he knows basic mechanics then there isn't any reason for a popular classic like the Capri to be expensive to look after.