As a person who already had worked on the Lab C part of this Biodome Complex, I can definitely say that you certainly can put the labs through C01 ~ C06 (the part you have not decided whether it will be D or I) on the I part. You will not excess the entity limit.
If you were to merge this part with the I map, then this little hallway that connects the Lab C and the lobby would have to be a loading zone. But I’m not sure if that would be a good idea. This hallway would seem more appropriate to be “open”, somehow, with transparent glass doors, etc. Yeah, you could put that cold, opaque, gray steel doors, but I don’t think such metally-secured door is fit for this hallway part. You can see this hallway leads to this square room, housing two bathrooms and access to parts of Lab C with two decon silos. With that I believe this little square room act as a sort of mini-Lobby, a place free from high security restriction(?). That’s sort of like how some parts of Lab A has this canteen, office areas, bathrooms etc before you go through decon labs which start to have more sinister experimental labs in it. If that is the case, the hallway would be more appropriate to have transparent glass doors rather than secured metal doors, which would be inappropriate for level transition parts.
That’s just my thoughts, so don’t get carried away too much.
A bit off-topic, but it always bugged me that the door connecting Lab D and Lab C is clearly labeled as decon area but in-game they used a normal steel door which doesn’t really fit at all. I always imagine a decon door to be these massive blast door, but for some reason it’s very… unique that that section of the map use such a normal-everyday steel door for decontamination area. I’m curious on what you think (and if you will “change” it, although I doubt). Honestly, I think the Lab C was designed not “seriously” enough, since it is never supposed to be explorable in-game. The A15 lab is another of issue where an entire lab blocks a hallway. Wouldn’t make a sense design-wise.