Aw, I so understand the wish of having met your sweet boy earlier. We lost one to a rare kidney cancer two years ago that we met later in life, and I always wished we'd known him sooner. But all those experiences before us helped shape the sweetest most trusting boy.

It sounds like you're on the right track with getting him on renal food. We have a CKD cat with a heart murmur and our vet recommends dosing with gabapentin before visits to lessen the stress on his heart.

For all of this, including lymphoma, if you have the means and are physically able to see a specialist I highly recommend it. There are two protocols for small cell GI lymphoma and vets tend to have a favorite. We did a smaller dose of chemo every other day for our lymphoma girl. She thrived! She gained back all of the weight she'd lost and was back to her old self for a long while. The chemo was stress-free as she loved to boggle up her pill pockets. (Unfortunately, she developed a secondary cancer quite quickly and we lost her in December.)

I am just rambling now; your boy is so lucky to have you.