I'm especially sus about how they might define whether what I create during the period of employment, in my own personal time, on my own hardware/software, is relevant to the business operations and therefore they can lay claim on it. When my tasks are so vague.

I get that IP clauses are not uncommon (although not present in my previous contracts!) - but the way they've worded this really grinds my gears because (a) they rely extensively on open source software and have never spent a red cent contributing to it, and (b) a good part of the solutions I've come up with for the business have been based off publicly available code and answers on stackexchange, github and the like - from people helping each other out on their own time (Much of that extra research being shit I've learned on my own time as well)

Now they want to turn around and potentially stop me from giving back to those same communities? Grrr.

Fully agree.

I might just start with suggesting alterations but I suspect I might not get a straight answer out of our hideously incompetent business mgr (this contract was sent through as late as possible!) I feel like I'd benefit from professional opinion just do a once over and say 'eh this is OK with a few tweaks' vs 'this needs major changes', to back up my position (or help me decide to just bail).

$400 is definitely going to sting, but I don't want this to impact what I want to do after I leave... Maybe I should just look for another job.