Below is a image showing the prerequisites for each HQ level. Your primary focus for construction should always be to the prerequisites for upgrading your HQ.
Beyond that, you need your gear factory at 20 so you may upgrade your gold hero gear beyond level 40.
Your iron, coin, and food vaults should only be leveled for VS and Arms Race points.
Your component factory, smelters, material workshops, iron mines, farms, and gold mines should be leveled to 20. Beyond that you get diminishing returns.
Training centers should be 20-25.
First hospital needs to be leveled to 25 but the other 2 can stop at 15.
Squad pads and tavern should be leveled 10-15.
Builder’s hut is debatable but 20-25 is reasonable.
First tech center, tank center, and one drill grounds need to keep up with your HQ. Second tech center and other drill grounds should be 15-20. Aircraft and Missile centers should be leveled up when you have openings available as they strongly increase your power depending upon your squad make-up.
Alliance center needs to be leveled up to 23.
Barracks are the most complicated. The first one should be leveled up with your base for maximum level troops. A second barracks at maximum level for troops is helpful but optional. The third barracks should stop one level below maximum troop level and the fourth barracks one or two levels below maximum troop level. By this I mean, if your maximum troop level is T8, then first barracks at T8 (level 24), second at T7 or T8 (level 20 or 24), third at T7 (level 20), and fourth at T6 or T7 (level 17 or 20).
When I say “First” I mean the structure with the highest level survivors. When you quick deploy, it will assign the gold and purple level survivors to the “First” one, the purple and blue to the second one, etc.
Your alert tower and recon planes only take a few seconds to level and should be kept at maximum.
As you level past HQ 20 your rss requirements skyrocket so its important to conserve them to focus on leveling your HQ.
Exceptions to the recommendations above would be to level things up for Arms Race and VS points.
