How do I buy big time on Coinbase?

Excuse me, as a cryptocurrency enthusiast, I'm interested in purchasing a significant amount of cryptocurrency on Coinbase. Could you please guide me through the process? I'm aware of the basic steps like signing up for an account and linking a payment method, but I'm specifically wondering about the best practices for making a large purchase. Should I break it down into smaller transactions? Are there any additional security measures I should consider? Also, would you recommend checking the market conditions before making such a purchase, and if so, how do I do that effectively? I'd appreciate any insights or tips you could offer.