Overall, the information you've gotten is correct. There is one very important caveat. Ketones/DKA trumps absolutely everything. DKA is one of the most challenging issues anyone here has to contend with. Trace ketones can develop into full blown DKA in an astonishingly short period of time. And as I'm sure you know, it's life threatening and expensive to treat. So, we want to help you avoid a repeat.
Testing regularly for ketones is essential. (You're obviously doing that.) IF trace or greater ketones show up (I'm not sure if you're testing for urinary or blood ketones -- urine strips or a meter), then following a dosing method may not apply. Ketones appear if there's not enough insulin on board, there's some source of inflammation or infection, and your cat isn't getting enough calories. Given how close the episode of DKA was for SP, I would not be looking to reduce the insulin dose too soon. (This is another reason your vet's suggesting a sliding scale dose is not a good tactic -- well, that and it will cause Lantus to give you wonky numbers.) Rather, if you see numbers are dropping, prop them up with food as best you can.
Given the recency of the DKA, if you get a low pre-shot number, I'd encourage you to post rather than skip or deduce the dose. For example, on 3/7, SP's PMPS was 103. You reduced the dose and by +2, SP was at 221. A different tactic would have been to stall without feeding your kitty. If over the next couple of tests (e.g., you want to test every 20 - 30 min) and if numbers are rising, it's likely safe to shoot. Ultimately, if you are following TR, you will get comfortable shooting progressively lower numbers.
Also, a piece of housekeeping: You might want to change the title of your spreadsheet to something like "SweetPea's Spreadsheet." The spreadsheet itself is titled "FDMB World/US 12/12 Insulin Spreadsheet Template FOR PET METERS." I'm hoping you didn't save your data to the original template!!