Welcome.
Good insulins are the human Lantus and Levemir and the pet insulins ProZinc and BCP PZI. For those two human insulin it is best to get the 5 pack of 3 ml disposable pens via a 10 ml vial. Although per ml the vial is less expensive most cats will not use up a 10 ml vial before the insulin goes bad/becomes ineffective. The human insulin N/NPH is sometimes prescribed but only lasts 8-10 hours. Same for the pet insulin Vetsulin/Caninisulin.
Most of us here test or cats blood glucose at home using a human meter. We test before each shot and periodically between shots. We record our reading and other info in a spreadsheet. See:
http://www.felinediabetes.com/FDMB/threads/fdmb-spreadsheet-instructions.130337/
Home testing negates the need for a vet visit for BG measurement. Also, vet stress can artificially raise BG by 100 (USA) or move points
A low-carb canned is best. No reason for a prescription food. Here is a list of commercial low-carb canned
http://www.felinediabetes.com/FDMB/threads/shortcut-shopping-list-all-8-or-less-updated.117688/
Here is a link to home testing blood sugars
http://www.felinediabetes.com/FDMB/threads/hometesting-links-and-tips.287
If yo have any question please post in the Health forum
http://www.felinediabetes.com/FDMB/forums/feline-health-the-main-forum.28/