30s couple - looking to take advantage of favorable situation

Hi everyone! Using a throwaway for privacy. My wife and I are in a privileged financial position and want to make the most of it, with an eye toward the future, including possibly kids. Current situation: Mortgage: 4.5%, 25-year term. Payments start in ~3 years Fixed rate for first 3 years, and then re-adjustment with the bank. Liquid Assets: - 40,000 EUR in cash - 34,000 EUR in checking accounts Investments: - 4,000 EUR in bank-tailored stocks - 16,000 EUR in Core World ETF (through app) - 23,0