(Gah, gah, gah, just realised I edited instead of quoted Degausser's previous post. The danger of moderator privileges. While I see if there's any way to get that back, here's my take in a separate post as I intended ...)
My take ...
1) I admit I've rarely had trouble with the intellect devourers, given the game does give you that hint to stay at range, but hopefully Larian have been collecting game data and will rebalance if evidence is that folk have found it problematic. And worse comes to worst, hopefully there'll be difficulty settings in the final game, though people having to mess around with difficulty settings due to odd difficulty spikes is certainly something games should be trying to avoid.
2&3)I've never seen these bugs. It may be worth submitting them with your save file to Larian support via their
form, though obviously the version of the game they're now working on is radically different from the patch 9 we're still playing so it may not be relevant any more. Your call!
4) This probably is related to the known bug with overly sensitive NPCs in patch 9 (the deep gnomes in Grymforge have also caused many folk problems), so it's reasonably safe to say we can expect a fix with the full release.