Is it permissible to collect the remaining Zakat funds each year to form a large sum, with the aim of helping the needy with major projects such as marriage, housing, or starting a business, knowing that these funds will only be spent on these designated categories?

It is not permissible to delay the distribution of zakat (definition) after it becomes due, except for a valid excuse, such as the absence of eligible recipients or the unavailability of the wealth. What you have mentioned is not an excuse. Therefore, you are obligated to distribute all of the zakat when the Hawl (one lunar year) is completed.