My advice would be to buy ball-joints and motor mounts. A tubular k-member won't solve any of those problems unless you buy tubular control arms that come with new ball-joints. Motor mounts and ball-joints are not expensive. Motor mounts are simple to replace, and I'd think doing ball-joints would still be far easier than replacing a k-member.
Scratch my previous statement. If your control arm bushings are cashed, you'll probably be time ahead just putting in new control arms (assuming they come with new bushings and ball joints). Good time to do this if you are replacing springs anyway.
Get the 'vert motor mounts.
No reason you have to run isolators if you don't want to. My car doesn't do anything strange without them in.
I still say the k-member is not a good use of money.......in that there are a lot of other places most peoples cars can use help. How's you're posi doing? $50 buys a rebuild kit, and it's easy to do. How do your tires look? I'd put money many places before in a part that really offers nothing but minimal weight savings.