You may do each of the following, in order. In these steps, "pre-existing" means it was there at the start of your activation:
Place a sleeper token on one planet that has ground forces but no sleeper token.
Convert a pre-existing PDS into your flagship.
Convert each pre-existing sleeper token into either:
- A PDS
- A Mech and an Infantry
If you have a planet with just an infantry, it takes 3 activations of the sector to make your flagship through this ability chain (add sleeper token -> convert sleeper token to PDS -> convert PDS to flagship).
From the Rules Reference on Timing:
If the timing of an ability uses the word “before” or “after,” the ability’s effect occurs immediately before or after the described timing event, respectively.
If the timing of an ability uses the word “when,” the ability’s effect occurs at the moment of the described timing event. Such an ability typically modifies or replaces the timing event in some way.
Effects that occur “when” an event happens take priority over effects that occur “after” an event happens.
From this, we have the following order of triggers:
Scanlink Drone Network triggers first, which modifies "activating a system" to include an exploration of one of that system's planets.
Terragenesis would trigger next, following the completion of the exploration component of the activation of the system. If you don't have a sleeper token, the planet would gain one.
Awaken and Ouranos trigger third, following the completion of the modified activation. You can resolve them in either order, but given they (unfortunately) don't interact, it's always better to have Ouranos trigger first so that you don't hit your PDS limit. Ouranos requires you to have had a PDS in the system when you activated it. You can choose to turn one of your pre-existing PDS into your flagship. Any PDS created with Awaken this turn can't turn into your flagship because they weren't there at the start of the activation (Ouranos says "you may replace 1 of those PDS").
Awaken requires you to have had sleeper tokens on at least one planet in the system when you activated it. You can only use Awaken on sleeper tokens that were there at the start of your activation; tokens added by Terragenesis can't be immediately awakened because they weren't there at the start of your activation (Awaken says "you may replace each of those tokens").
For each PDS you place with Awaken, Hecatoncheires triggers, and you can replace the PDS with a Mech and an Infantry.