Sounds like you're approaching it sensibly, with your mentality I'm sure you can find the right car.
I was just about to post about suspension but Jared ninja'd me... I'd start with shocks and bumpstops, springs only later if required (this is certainly economical if it's DIY, otherwise perhaps not?).
Yes, bad bumpstops are a crazy issue with this chassis, a black mark on BMW. Replace stock ones with the BMWP shorter ones, there are many brands, you shouldn't pay for BMW branded ones.
Edit: Heavy steering? No, not a common problem, possibly related to the PS leak?