OK, I'll go first
Rear differential: Mine has been seeping for years but never actually saw the oil level go down. If it is only slightly oily, don't do it now.(or ever)
Same for power steering gearbox.
Front flex disc cracking: That would be a priority. This problem generally result in drive train vibrations. I'd do it now, it is relatively cheap.
steering shock leaking: Do it now but not at $190. Buy the part at the right place for about $50.00 and any half bright rookie mechanic student can replace it less than 15 minutes.
oil leak from timing cover/head gasket ($1200). How have they diagnosed the faulty head gasket? These engine are leakers (front top timing chain cover), very rarely from the head gasket at this location. Get a second opinion on that one. How much oil does the engine uses?