How do people structure their payment terms on larger jobs?

I assume its some combination of an upfront payment, progress payments with completion, and something on the back end. Would you progress payment based on completing some of the big elements? What is a fair amount to hold to the end?

We are gearing up for the big project ($50K+ range) which will include a retaining wall, fill, a patio, stairs, a flagstone path, and a ton of new plantings (like 1500 sq ft), likely some landscape lighting.

Here is the plan which I have posted before in a thread on finding contractors, if anyone is interested.

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