4a I enlarged my works:

Having explored actions of the mind and then actions of pleasure and stimulation, the collector of sentences advances to part 3 of the experiment, growing his property.

גָּדַל gaw-dal’ – grow, advance, became greater, enlarge
מַעֲשֶׂה mah-as-eh’ = work, property, business, possession

4b I built houses for myself, I planted vineyards for myself;
Solomon investigated action related to architecture and building, growing and managing produce.
5 I made gardens and parks for myself and I planted in them all kinds of fruit trees; 6 I made ponds of water for myself from which to irrigate a forest of growing trees.
The Qohelet increases and investigates the management of all kinds of orchards and horticulture. Water management is examined as the preacher creates ponds and irrigation for forests and as well as cities.
7 I bought male and female slaves and I had homeborn slaves. Also I possessed flocks and herds  larger than all who preceded me in Jerusalem.
II Chronicles documents that Solomon took many slaves. “7 All of the people who were left of the Hittites, the Amorites, the Perizzites, the Hivites and the Jebusites, who were not of Israel, 8 Solomon raised as forced laborers to this day.” The homeborn slaves would not have been Israelites. Today our culture is opposed to slaves. Even if the slavery referred to here is not the chattel slaver we had in the United States of America we still take note. The cultural difference is magnified as animal and bird husbandry are lumped together with slave husbandry. That aside, the Qohelet investigates and possessed many forms of animals and their care.
8a Also, I collected for myself silver and gold and the treasure of kings and provinces and the treasure of kings and provinces.
II Chronicles has the following, “15 The king made silver and gold as plentiful in Jerusalem as stones, and he made cedars as plentiful as sycamores in the lowland.” Even if hyperbole, he gathered a lot of gold and lumber. I Kings is a bit more specific, ” 14 Now the weight of gold which came in to Solomon in one year was 666 talents of gold, 15 besides that from the traders and the wares of the merchants and all the kings of the Arabs and the governors of the country.” This is over 750m in todays money.
8b I provided for myself male and female singers and the pleasures of men—many concubines.
Bodily pleasure was included in part 2 of the experiment. Here, after mentioning getting wealth from other kings and governors, concubines and singers are property. This concludes part 3 of the experiment.
Scripture quotations taken from the NASB. Copyright by The Lockman Foundation (NASB®)