how to repair combo 1.7 deisel faults?

i have just bought a 2002 1.7 desiel van and im have a few problems. the van will not go over 4000 rpm. i had a friend plug in a diagnostic machine in and it said i have various faults

1: main relay fault in circuit
2:exhaust gas re circulation no communication
3:boost pressure solenoid valve no communication
4:glow plug heater circuit (a) no communication

need to no how to fix it and if it can be done by myself or will i need to take it to a garage.