(oh dear. I dont think ive visited these forums since amfp was first out)
In Simon's apartment, if you look underneath the waste basket in his bathroom, there will be a couple of what look like bloody rags. I can imagine he's woken from nightmares a few times to find his head bleeding. Fun times.
The Construct is great. Easily my favorite enemy, mostly due to its design. It can also float, apparently. I piled a ton of crap at the top of the stairwell it comes up (if you decide to summon it). After pulling the level, the monster's walking animation continued as its body simply floated up and over the top of the pile. What a truly majestic creature.
Presuming you spawned the Construct, it will despawn as the door to the communication center is closing. You can then immediately open it again and explore the now powerless hub area at your leisure.
If you do decide to return to the hub, you can examine Carl's powered down Mockingbird. It will be unresponsive, but you'll still get a little bit of static/feedback at close range. Not super reassuring, but might help if you think you killed him.
The first "I need an Adult" unit you meet directly after escaping Upsilon is not overtly aggressive. It will only attack if you run up to it. Otherwise it will just follow behind you, saying creepy things. If you approach it slowly, it will even back off a bit, keeping you at a distance. (Based off two runs where I've approached it. The one close to the sunken boat will sometimes attack you on sight. Other times it will be twisting in crazy circles above my head by the time I reach it and completely ignore me)
On the Curie, after sneaking around the Flesher and reaching the wheel operated ladder, continue down the hall. In the room to your (left?) there are a couple of lockers. One contains a small surprise!
At Delta, you can take one of Aker's eyes back out into the ocean with you (if you really want to). It sinks. The K8 doesn't seem to find this creepy either.
If you go to Theta's side entrance before unlocking the main gate, Simon will say something like "Why am I doing this? This is kinda dangerous and unnecessary." :Y