Hey edog, thios model is actually fully constructed at the moment, minus the tracks. As for your questions...
1) The Tamiya Tool set is to scale. The #7 tool is for Tigers and King Tigers, as well as for Brummbars. The #5 tool is for all other Panzer III's, IV's and Panthers. My advice on painting the zim to have it stand out, is to first basecoat and camo your model. Then give the zim a wash (oil, enamel or acrylic is fine), then after the wash dries, dry brush the zim on it's high points with the respective lightened basecoat. This will darken the recess areas, and hightlight the raised, thus bringing attention to your zim.
2) The normal ratio for the Polyester putty is about 50 parts putty to 1 part catalyst. The more catalyst the faster the drying time, and vice versa for a longer drying time. With a 50:1 ratio, you will have a solid 10 minutes before th putty becomes unworkable. Which is more then enough time if you are using the Tamiya tool.
As for purchasing the putty, I get mine through my locol hobby store, which carries all Tamiya products. 1 tube of putty is enough to zim up at least 4 King Tigers.
Cheers
Rob