If it was me...I'd offer the seller 3K and no more.
You WILL be spending a minimum of 2K in repairs within a few months on the repairs you mentioned. Count on spending twice that for other repairs you don't know about at this time.
It's an 11 year old car going on 12.
I would not swap out the rear self leveling systems for regular shocks....
I look at it this way and most don't agree....if I can't afford to fix it correctly....then I have no business in owning one.
You fix it correctly..it will last you for many years to come.
I have a 18 year old 140...original owner....and never have had serious issues with it.....engine and tranny...never a problem. Radio issues, window reg issues. No a/c issues. Luck I guess!