I didn't notice crash damage from the mini CZARs, either the shields absorb all of it, or the area is so small it needs to land right on top of a building
The main threat they pose for defenders' bases is that they'll deplete shield generators quickly by trying to shoot down air units under them, so you need to be careful not to hide your air when your base is already threatened. An option to chose how many of them can spawn at a time, and how often, would be nice. As for the unit itself, it seems balanced to me as it does exactly what it's meant to do. I usually kill them with T4 turrets or T3 ground units, I haven't tried ASFs yet so I can't say, but 28k HP doesn't seem overwhelming.
I always disable nukes, except for the defensive ones (I like these) ; the ones I get are those built by the AI itself (they usually target roaming T4s though, not my base). I like the idea of having to defend against more and more nukes, but I'm not that good at survival maps in RTS in general so I prefer focusing on ground and air armies. As for T4, I think it's because most of the time they somehow get stuck in the HQ base, but recently the AI seems to remember how to send them. I don't think they're from the survival waves though, it's more likely the ones it builds once it gets enough eco.
I'm gonna try AI controled waves next, I'm curious to see how it'll behave !