You can get this achievement shortly after you gain control of adult Arno (after you retrieve the watch from the butcher). Firstly, go to the map
and take note of the two viewpoints. Now go synchronize them both in typical AC fashion. Once that is done, you have but two more tasks ahead of you: find the chests in both halves of the district and find the cockades.
The chests are simple enough; they should all be marked on your map now. (Note: you do not need the blue or yellow companion chests, only the grey ones). My strategy was (is) simple: highlight a chest on your map, venture to the location. If the chest is light grey, it means that it is not on the same plane as you i.e. higher or lower. Simply activate Eagle Vision
and scan the area. Conveniently EV sends out a pulse that will highlight the chest regardless of the level it's on. Repeat this for all chests.
I have but one caveat in regard to the chests. Some of them are guarded by 3 soldiers. Arno, not being an assassin at this juncture has access to only a basic sword and parry. Before going after the guarded chests, I suggest you go to a shop, house icon with an F, and buy a full stock of medicine. Following this, venture in and kill the guards by spamming
and throwing in a few well-timed parries with
. (The guard's weapon will glow). Use
to roll away from attacks by the axe-wielding heavies. When you take damage, simply spam
to heal accordingly. It is highly unlikely that you will go through five vials in a fight, but restock if needed.
Finally, the cockades. These are small tricoloré buttons that often rest on wires. The rub: they only appear on your map, mini or otherwise when you are close to them. Thankfully many of the chests are in their vicinity, but I have attached a video showing their exact locations for reference. It contains the chests as well, so you may have to scroll through a bit.
On a final note, I would do this before you finish Seq. 1, as I am not sure the soonest you can return to the Recollects area of Versailles, if at all.
Edit: It would seem you can fast travel to Versailles, noted by a large V, during Seq. 3 with better gear. Thus, this is simply the earliest you can achieve it.