Hey stinger, the Tamiya M4A3 actually comes with decals for a tank of the mighty 4th Armored Division -- Patton's killer armored vets. The model itself is old and has a few problems, but it's still a good enough kit. Just one thing. Leave the applique armor off. M4A3's didin't use it. Other problems are for the armor purists only.
For the Panzer, I'd suggest a Marder! Marders were used to great effect in the Desert -- so why not use Tamiya's great kit (the Marder III -- the one with the Russian 76.2mm gun)? It even comes with 15th Panzer Division decals, and instructions on painting the neato sand over grey camo pattern. You can see inside the fighting compartment, which is great in this case, as the stuff inside is cool.
(Don't use the Marder IIIM --which has the fighting compartment in the back. Use the Marder III, with the compartment in the middle, and the Russian gun. Those are the ones sent in lergest numbers to Rommel's crew.)