Guillain-Barré syndrome — IVIG vs plasma exchange, criteria for ICU admission and intubation?

55M presents with progressive ascending weakness over 2 weeks. Started with bilateral leg weakness, now involves upper limbs (MRC grade 3/5 all four limbs), absent deep tendon reflexes, and autonomic instability (HR 38-140 fluctuating). Albumino-cytological dissociation on CSF: protein 1.8g/L, WBC 2/uL. NCS confirms acute motor demyelinating neuropathy. FVC 28% of predicted. Per EFNS/PNS 2023 GBS guidelines, should I start IVIG (2g/kg over 5 days) or plasma exchange (5 sessions over 10-14 days) as equivalent first-line? Should I admit to ICU given FVC 28%? What FVC threshold mandates intubation?