I am a huge believer in the best defense is a strong offense, so yes, I would do all I could to get info and get out in front of whatever is coming your way...particularly if the person you talking about is BM or a skid

When you try to get ahead of someone you view as a toxic person and make guesses at what offense they might make and in the process you are mentally making them act negatively towards you over and over again.  It becomes a self fulfilling prophecy because in your mind they have wronged you so many times that even if what they do next is NOT designed to intentionally cause problems you will view it as if it was.  Unfortunately, I do see evidence that you are already doing this.  Every action by your Skids or BM is automatically put in the bad bucket... whether it is.. or was intended to be that way.  Yes, I know they have not been great all the time, but honestly there are a decent amount of things I see you have posted about that you either blew out of proportion or were actually valid/reasonable actions on their part.

So, in your case, I think you would well benefit from trying not to run through scenarios in your head.  It's like having an argument but carrying on both sides of it in your head.. or waking up from a bad dream and being angry at your partner for something that happened in the dream.  It's keeping you in a high state of anxiety and increasing the number of slights that you mentally feel you have been subjected to.

That being said, if you have a good reason to believe that someone is going to do a specific thing.. it's not bad to plan accordingly.  Like, you go to a function where BM will be.  It's ok to think about tactics to avoid her or deflect her if she tries to engage you.  If you have concrete reason to believe she is going to try to change custody agreements.. gathering proof of your DH's involvement with the kids isn't a bad thing.  But... only if you have specific targeted issues.  Don't keep running all the what if's through your head.. you will make yourself crazy.

When somebody has wronged me i information gather first. Make nice with the people who know about her(DH, Mil, ) research on Fb etc. After i find out as much as I can I make a plan of how to act with those people who affect me in response to that persons actions.

How do I protect my assets? How do I protect myself? My kids? My Dh? My family pet(lol. .but in a crazy BM world it might happen...)?

Sometimes I poke the bear to see how it will react(such as say things in a certain way i think will get a rise out of toxic person etc.)

So not necessarily stay ahead but see how accurately I can anticipate reactions by said toxic person. Then I selectively choose what they hear etc.

Well sounds kinda crazy  i assure you it isnt.

I am finding that as long as there is some way BM can harm you in some way, you stay alert.  CS ended and all ties ended in June in our case.  She can't really do anything to us anymore.  She's already alienated 3 of the 4 skids, but having dealt with that already, if it happens with the last one, we will have coping skills at hand.  

I will say its weird to adjust to this new realization.  Letting go of that constant watching and preparing for the worst is a heavy weight to carry but life is getting much lighter everyday.  

Learning everything I could about Cluster-B and learning BM's patterns helped me to predict and to let go during her reign of terrror.  It is a lifestyle that only other step parents with a HC birth parent can understand.  It can be a lonely life at times and you have to work around that aspect.  I think my answer to your question is to do both, find a way for balance between the two so you can enjoy the life you have now and get to the life you will have when she has no more power to manipulate you life.  

I think you have to take both approaches. You have to have enough information to set appropriate boundaries and recognize when sh!t is about to hit the fan. You also have to know when little things don't need to be something you worry about.

BM wants DH to go to dinner with her? Ignore. Let DH handle it.

BM threatens court? Give a minimal amount of thought to whether her claims are justified. If not, ignore. If so, talk to DH and act in a manner that protects you.

BM tells skids to snoop? Be active. Hide things you don't want the kids to see/take pictures of/have acces to. You won't be able to stop everything unless you leave, but you can at least minimize the damage.

Everything doesn't have to be a battle. All because BM threatens something or says something doesn't mean it needs additional action. Unless it has a direct impact on you, make a mental note but don't engage.

My DH's EX used to threaten to take him back to court countless times.  He if he was ever late with CS (crap happens.. it was a blue moon event etc).. if he refused to pay for one of her whims... when CS ended and she wanted him to pay for HER health insurance or she would take him to court for reserved spousal support.  You want to know how many times we ended up in court?  Exactly zero times.. so each and every one of those were basically empty threats on her part.  Does it mean it didn't raise my BP?  No... of course you have to entertain the possibility that THIS time she isn't crying wolf... but it's helpful to not project and run through scenarios in your mind on an endless loop.  In the end.. you are even worrying about things she USED to do... and at some point, you need to trust your DH will come to you with issues that will impact you in some way (including household finances and visitation issues).  And.. with concrete issues not wishy washy random kvetching at him and talking down to him. 

Your DH needs to stop using YOU to vent when his EX gives him Hell... because that is all she is doing.. and ya know.. he is a big boy and should be able to handle that himself and just thank his stars he is no longer with a harpy like that.

I don't know how you can ignore toxic people's behavior if they're really toxic! Of course, expect what's to come and try to mitigate the likelihood of those results. Who wouldn't do that?

BM should not be any where near your house. Closed to your house is the curb, any closer call the police and file trespassing.  NO BM, BF dinners. There is email to settle any problems. NO talking between them, you want hard copy’s of all communication. It’s your DH problem for playing her game.  BM is going to fill kids heads with her SH*T you can’t stop that.  You may never get any loyalties from SK  so don’t sweat it. Disengage  

because she is so toxic and aggressive it's a case of mostly ignore but... ALWAYS take a deep breath, never give an answer outright to ANYTHING. Always have a good think on it if you are going to have to engage in any way. Being one step ahead is almost impossible when they are like slippery eels and lie and deny. But it has been accomplished. It's all hard work so ignoral is the best option in the long run, despite the feelings of wanting to put her right etc on her lies, it just isn't worth it because thats what they want: more supply more fuel more attention.