This mission dives you straight into the deep end and you are constantly attacked by enemy units. Your villagers are working out of the fort (top of your screen), while you are trying to defend your base inside the walls.
The goal is to try hold out until the cavalry arrives, I recommend building 5 of each unit from the barracks outside the fort, take them up to the top left hand of your screen and wait for the trigger to light the signal fire (you will need villagers to gather the wood).
Enemy units will try take out your villagers but if you have enough units to defend them, it should be enough for the villagers to gather the wood stock pile.
When the villagers have gathered all the wood stockpiles, the cavalry units will arrive and drive off the remaining enemy units.
Apologies for the shortened video, had some technical issues recording the remainder of the mission. I will redo the mission and add in a new video.
You start off with a reasonable size army to defend your base. Build up your army (Hoop Throwers are decent units and training 10 helps with a secondary objective).
Build Fishing Boasts to fish for Food (There is no real threat from the sea so no need to waste your resources on a naval fleet).
Try claim all treasures and supplies to get resources quicker.
Once you have a good sized army (5 of each unit plus 10 x hoop throwers), destroy their bases and move into the mines to destroy the enemies remaining units and weapon caches.
Build a strong base and 20-30 units to defend your base.
Building a large sized Naval Fleet is the key to winning this mission and achieving objectives. (You do receive a Galleon every couple of minutes or so, try save up as many Galleons as you can.)
The enemy base is well protected just west of your starting position, try attack them from the south and build mortars to take out their Outposts and Buildings quickly. Support the artillary units with cavalry and crossbowmen.
Galleons also provide training units, get the Galleon close to a shoreline and build units to support your main army.
Build up an army (30-40 units) to quickly defend against increment attacks from the enemy force.
For the Secondary objective, you only need your main warship to take down the enemy fleet and docks.
Destroy their ally (native) buildings and rebuild a trade shop to get access to additional units and technology.
Artillery is advantageous to take down the enemy buildings from range.
Build up an army (30-40 units). Cavarly is ideal for this scenario to take down enemy artillery and to move around the map faster
Use your cavalry to rescue more Aztec soldiers.
Outposts and Town Centers build near the temples is not a bad way to defend one temple while your main army defends another temple.
Trying to save all the temples may not be the best option, focus on one temple if you do not get off to a good start.
Completing the secondary objectives to gain more experience will help quicken the mission.
Cavalry and crossbowmen will be advantageous in this scenario.
Reopening the trade route (defeat the enemy army and build a trade post)a nd upgrading the routes will be the best way to gain experience faster.
Build up your army (80-100) units. Artillery is a big key to destroying the forts and enemy buildings. Provide 40-50 Cavalry and infatry units to defend your artilley units.
A large naval fleet is advantageous to attack the enemy's docks and forts from range.
You get a sizeable army at the beginning of the mission. Destroy the enemy units guarding the Fixed Gun.
The Fixed Gun is a major key in destroying enemy ships and the Fountain of Youth. Defend it at all costs.
Building a trading post may help distract the enemy's main army. Use the fixed gun to shoot at the Fountain of Youth.
I attempted to try destroy the enemy's main base but you waste a lot of units and resources trying to destroy it. Focus on defending the gun and having a 30 naval ships to concentrate their attacks on the fountain of youth.