Imagine you are managing a quantitative trading strategy and need to execute a large stock order, equivalent to approximately 20% of its Average Daily Volume (ADV). How would you design an optimal execution algorithm to minimize total transaction costs—including both explicit and implicit costs—while carefully considering market impact, liquidity, and any time constraints? Please elaborate on your methodology, key considerations, and potential model choices.

假设你管理一个量化交易策略，需要执行一个占市场日均交易量很大的股票订单（例如，相当于日均交易量的20%）。你如何设计一个最优执行算法来最小化总交易成本（包括显性成本和隐性成本），并考虑市场冲击、流动性和时间约束？请详细阐述你的方法论、关键考量因素和可能的模型选择。