A320 First Officer reported encountering navigation system failures after departure that would preclude RVSM operations and there was insufficient fuel to complete the flight. The flight crew diverted to another airport and made a normal landing.

Narrative

We operated an Airbus A320; on a part 91 ferry flight from ZZZ with an intended destination of ZZZ1. The flight was dispatched with an inop ADR 3 (Air Data Reference) compliant with the aircraft's MEL; provided that IR1; IR 2; ADR 1; and ADR 2 are operative. They were. Shortly after take-off; we began receiving a stream of amber ECAM messages. Messages included VENT Blower Fault; NAV ADR 3 Fault; AUTO FLT AP OFF; and other navigation-related faults. After complying with ECAM procedures; and troubleshooting; we determined that we could not recover the autopilot. As the autopilot is required for RVSM operations; and as we planned to climb to FL390; we realized that we would have insufficient fuel reserves at ZZZ1 flying at FL270 with the higher fuel burn. We elected to return to our point of origin; ZZZ1; for repairs. While descending into the ZZZ2 airspace; we were aware of significant VFR traffic at ZZZ3 and other VFR aircraft operating in the local area. When we requested vectors and a descent for landing at ZZZ2; ZZZ Approach Control advised us that our dispatcher requested we divert to ZZZ. In what appeared to us to be an encouraging tone of voice; the Controller asked if we were requesting priority handling. We affirmed; provided fuel and souls on board; and stated that we would not need Crash Fire Rescue (CFR) equipment standing by and that our problem was multiple indications of failures of secondary systems; and that our return to ZZZ was driven by the fuel problem that resulted from our technical inaccessibility of RVSM airspace. The landing at ZZZ was otherwise normal and uneventful. In debriefing this flight; we concluded that the multiple issues we encountered seemed to stem from the inoperative ADR 3.