A 65-year-old man with a history of hypertension and type 2 diabetes mellitus presents with a 3-month history of progressive fatigue and ankle swelling. His blood pressure is 155/95 mmHg, and his BMI is 32 kg/m². Laboratory investigations reveal a serum creatinine of 180 µmol/L (baseline 100 µmol/L), eGFR of 35 mL/min/1.73m², and a urinalysis shows significant proteinuria (3+). Which of the following is the most appropriate initial management strategy?