Hi Pete:
Welcome to the site. There is a wealth of knowledge and knowledgeable folks here. I'm sure they can and will be able to help you out.
I'll try to offer what I can to help you out on your questions below. I'm sure there are others on there who can help you even better, but, since I'm first to reply, here it goes:
Suspension geometry isn't great on these cars as you know. One low cost fix is the "guildstrand mod". You can read more about it here:
https://lateral-g.net/forums/showthread.php4?t=20492
Bump steer, to my knowledge won't be fixed with a rack and pinion. I don't believe it has anything to do with it. Bump steer is the changing of your wheels direction as it travels through the suspension travel. Ideally, you want 0 bump steer, so your wheels stay pointed in the same direction no matter where they are in the suspension travel. Bump steer can change the direction of your car on you as you hit a bump, go around a curve, etc and can cause you to reduce/ lose control of your car. not good.
To fix it, you want to improve the suspension geometry. doing this optimizes the camber curve and eliminates bump steer. this is where I believe the correct length and located control arms come into play. the taller spindles help change the geometry of the stock suspension by altering the location of the pivoting points in your suspension.
The coil overs allow for quick ride height adjustment and may possibly reduce unsprung weight. Also, since they are a self contained unit you may not need a spring compressor for spring removal/ installation. then again, if you're careful (and I'm not advocating it) it is possible to remove and install the springs on the first gen f-body without a spring compressor.
I'd do more searches on the aftermarket subframes. It seems from my readings that many aftermarket frames are weaker than stock. You can weld up the factory subframe for increased stiffness. you can also do other things like use solid body mounts, subframe connectors, roll cage, etc. all these things in combination will substantially increase chassis stiffness. These are the types of things i plan do do to my car.
I think with the above mentioned stuff plus some research on this board you'll find all the tips/ tricks to do what you want. many of the aftermarket parts are for show and convenience as well. Like you said, you want function, not looks.
People raced these cars long before all these trick components came out and were successful. Hand built fabrication and ingenuity worked for them. I'm sure you can do it, too.
Of course, this is my opinion. Everyone has one. I hope this is helpful.
-Brendon