Ugh your TR has done nothing but further whet my appetite to go back to Cuba before US interests completely take over and the island becomes covered in KFCs (like Asia is).
So coincidentally, I've pretty sure I've been to the resort you stayed at in Varadero a couple of times. Not in about 10-15 years since I was a vacationing Canadian, but given the Cuban approach to change, I doubt it's changed much.
Interjet is great for short hops, I've taken them from Mexico City to Puerto Vallarta before and would rank them higher than US carriers for customer service. I'd imagine the drive to Laredo isn't too bad. I've driven to South Padre Island a couple of times, and also to Eagle Pass (which is the US side of Piedras Negras). As you may have noticed there are unannounced CBP checkpoints on the northbound sides of many of the highways.