Is it permissible for a wealthy, unmarried Muslim man to dedicate all his wealth as an endowment (waqf) for the sake of Allah Almighty, stipulating for himself a portion of the endowment's income to cover his needs, and is it also permissible for him to take from it as much as he wishes to spend on other charitable causes? What is the legitimate (Sharia-compliant) way to achieve this?

It is permissible for someone who is not obligated to provide maintenance to endow all of their wealth while in good health, even if they do not have enough money to cover their expenses, or do not have enough money to cover the expenses of their dependents, provided they maintain good reliance on Allah, patience, and abstain from begging. It is permissible for them to stipulate that they be provided for from the endowment. However, it is not permissible for them to take from an endowment designated for a specific purpose to spend it on other matters.