Update: I finished the suspension refresh. All in all, it took about 12h (I'm not fast, and I record as well), 8h for the front and 4h for the back.

I'm happy that it's done. I expected a smoother ride after being done, but it's still harsher than my parents 2016 DS3 hatchback. Nevertheless, I'm not disappointed at the results:

• the most important thing is that the shocks are now dampening. I no longer fear for my spine at every pothole and no longer feel every crack of the road. I can still feel the big ones, but it's not harsh like it was before
• body roll is greatly reduced. It had excessive body roll before, it now seems to behave correctly (no real measurements, just a feeling there)
• there used to be a noticeable steer to the right when trying to go straight. It's nearly gone now. It still doesn't go perfectly right, but you really have to leave yours hands off the wheel for a while to notice it.
• the front used to have about 1cm ride height between left and right. It's now down to about 0.5cm or so. It's probably linked to the previous point, and there are probably other parts that would require replacement to go perfectly straight, but nothing really starring at me, and I'm happy enough with the current state (and my wallet is happy not to replace other parts)

Now about the parts:

• all the shocks were shot: I could easily compress them by hand with medium pressure. In comparison, the new ones requires putting my body weight on them.
• while the cracks in the front strut mounts seem big when you observe them while on the car, after taking the struts out they don't seem quite as big. But it's still deforming, so it's a good thing they got changed.
• the bump stops seemed fine to me. I replaced them regardless since I had new parts.
• actually the rear Bilstein B4s shocks came with bump stops. Those ones seem to have a manufacturing defect, since the metal washer did not fit in them. I used the new bump stops that came with the dust covers instead. They also had a flat centering washer, while the original is curved. I chose to use the original, which was in good state. It seemed to make more sense/fit better.
• the rear strut mount refresh kit is different from the stock one. I was not too sure how to properly mount it, if it was actually the correct parts, and the original one seemed to be in good condition, so I opted to keep the original and try to return the new ones instead (which were not cheap, the ones that are visually correct are 3x cheaper, 60€ vs 20€ for both sides)
• I'm glad I didn't spend an extra 86€ on new hardware. Everything was fine, nothing broke (there was just one of the triangular washer on the back that somehow was chopped, but it didn't impact its function). I'm cost-conscious, so it'll do.

On the work itself: overall, it was long but not terribly bad, except a single thing: getting the front struts in and out of the steering knuckle. That alone accounts for about half the 8h I spent on the front struts. I used ModMini video as a reference, which is NOT the book way to do it. He makes it look easy because he has a lot of experience, and perhaps the car he works on had more clearance. For me, it was a nightmare because of the lack of clearance, and I had to call a helper to make it easier (and even then it was hard).
The proper way to do it is to remove the lower control arm ball joint. Since I don't have an extractor (and couldn't procure one in time without getting my schedule out of whack) I tried the jackstand + hammer trick ... which was totally ineffective. If I have to do it again, I will definitely get the tool and do it the proper way. The 10 min you loose to take the ball joint and maybe drive shaft out, you get back by not spending 2h battling the steering knuckle.

Thanks a lot for all the advices, I'll definitely reference this thread if I have to do it again in the future, and I hope this will be useful to others as well!

Happy driving!

 

Glad you got it all back together and that it’s driving better than it was before!

Not that it matters now, but did you pop the tie rods loose at the knuckle? I think that’s the way I’ve done it. It allows the knuckle to rotate forward, and if you get it just right, it usually comes apart pretty easily (but not always, haha). Also, are you talking about the inner or outer ball joint? The outer just unbolts from the knuckle - no puller required.

 

+1 = What deepgrey mentioned about the outer ball joint. No need for a separator - just undo the 2wo 13mm nuts and not the large 19mm(?) center balljoint nut.
Just a thought:
In regards to slightly drifting to the right - Did you happen to check your top strut mount housings for crowning/"mushrooming"?
That could be a cause for the/your slight drifting to the right.
I think ModMini may have mentioned that in his vid and proceeded to pond them flat.

Before I added my strut tower reinforcement plates; I flattened the strut tower housing tops flat. My car drove straighter with no drifting.
I later had my alignment checked after mounting new tires. All was good.

Glad to hear you've managed to survive the task with a little bit of sanity left to spare!

 

Yup I did pop the tie rods out.

I'm talking about the outer and .... I only unbolted the big bolt under the lower control arm, and did not notice the ball join was only bolted to the knuckle /facepalm
That would have made things easier .... Oh well, that's a lesson for next time! Thanks to both of you.

Yes, there was no visible mushrooming, but I'll double check just to be sure and pound them a bit if necessary, thanks.