Is it OK if I increase Puddin's food amount? He's still ravenous and he's getting more than 500 calories/day currently. If yes, would this quantity increase affect his BG numbers much?
Are you weighing Puddin fairly regularly, like every week or two? I would use the scale as an indicator how much to feed him. You might also see if the vet has an ideal weight for him. Feed more or less to get him where he should be. Neko got around 230 calories. I told her she was not allowed to go above 15 lbs. She had some Maine Coon in her so bigger to start. Vet didn't want her below 13 lbs. Some acros can get very large. The problem comes if they get arthritis as one of the acro side effects, then any extra weight can really be a problem. When I started feeding Neko raw food, I found that it did a better job at filling her up, even though the volume was slightly less than that of canned. She got 4 oz of raw vs one 5.5 oz can of canned.
Is there a point where he will find some regulation despite the diagnosis? Even without Cabergoline in the picture? Will this continue to increase if the tumor continues to increase?
How regulated is more ECID. Our saying is that there is a dose out there for every cat. I have yet to see one who didn't start seeing better numbers at some point. Have you looked at spreadsheets of other acros or suspected ones? Take a look at Shooter as an example of one untreated and confirmed acro, Mini Purrl not confirmed but higher dose so probably. Malcolm (confirmed) was starting to make good progress before something else took him away.
I have seen an acro cat all the way up to 50 units of Levemir and 30 units of R (total 80) but still well regulated. Seeing a cat get up to 80 units is not common (seen a couple), and Puddin's spreadsheet doesn't look like he'll need to get anywhere near that high. That was just an extreme example of a regulated cat that wasn't treated.
Using R in addition to the Lantus might be something for you to consider. It's an advanced technique that someone would have to help you learn to use. It's a short acting insulin, duration about 4-5 hours, that lowers the BG enough to give Lantus a better number to work with. Typically you'd start on a small R dose given at PS time. Puddin has an unusually late Lantus onset, which makes giving R easier in some ways. R might be in and out before the Lantus onset.
Are you considering not giving cabergoline? For those that can, I would strongly recommend treating an acro. Back in my time, a lot more people could not because the only option was radiation therapy. Surgery came later and even more expensive and even harder to get. If you can treat a cat, the acro side effects can be reduced and delayed. Insulin dose can be reduced in a lot of cats, but over all quality of life can be improved.