I also picked up an Eduard PE set, aluminum barrel, and Model Kasten Workable tracks to complete the package (my bargain basement deal got rather expensive!).  As I began build it it became apparent that the Pak 40 needed a lot of work.  I opted to pick up a Dragon Pak 40 from Depot Train and Hobby (Great shop with great service!!!).  The Dragon kit came with all of the shells and ammunition cases seen in the photos.

The kit goes together very well as I built it in stages (back gun deck, engine/drivers compartment, and the chassis.  It was much easier to paint them in sub assemblies and then glue it together. 

This was my first experience with MK workable tracks and I absolutely loved them!  I used DML's workable' on the SdKfz. 250 and they fell apart several times while painting.  The MK tracks proved to be very durable and did not come apart during painting, weathering, or while attaching them.  In fairness to DML, I used an oil wash on them and avoided it with the MK's.  I painted them with Model Master acrylic raw umber, gave them a wash of MIG rust pigment in Tamiya acrylic thinner, brushed on the metallic edges with Vallejo acrylics and airbrushed a very light coat of Tamiya buff to finish them off.  Unfortunately, I forgot to allign them on the wheels before taking the photos (they are workable so some adjustment is required when displaying them).

I painted the vehicle with several light coats of Tamiya khaki drab and then shot Tamiya dark yellow over the top.  The camouflage was painted using artist's inks thinned with isopropal alcohol.

Weathering was done with washes and light dry brushing with oils.