I'm finally upgrading. I just reached the "Remove Obsolete Packages" screen and, while glancing through, noticed a few packages that I installed and do not want removed. It lists about 150 so I'd rather not keep 145 packages I don't need.
Is there any way I can say "Keep these 2 packages but get rid of the rest"?
Just leave all of them installed for now, and remove those that you don't need with Synaptic afterwards (you will be able to see their "Status" in Synaptic).
Example screenshot (thanks @htorque !) of Synaptic showing the obsolete packages category: