I hope this helps.
Our DDog was diagnosed with lymphoma in Jan last year, he was 10 - not sure what stage but presenting in all lymph glands (I thought he had an infected tonsil so it was a big shock for us too) - 2 or 3 I think.
We opted for chemo - the COP protocol, which is steroids, plus chemo injections and chemo tablets.
The first month is pretty intensive - 1 injection a week for 4 weeks, plus tablets and steroids (be prepared for disturbed nights as the steroids will make your dog very thirsty and they will pee for England for a few weeks!).
If your DDog reacts to the chemo injections, you may need anti-sickness tablets as well - we did, but not all dogs do.
You may find that your DDog feels a bit odd on the day of the injection but this should pass pretty quickly.
DDog went into remission after the second injection and has remained so since. His course of chemo ended at the end of August last year and so far so good. He is full of beans and looking really well.
I will just add that any chemo treatment is designed to put the cancer into remission, not to cure - so at some point it will come back (and I am aware that our DDog is already on borrowed time).
We have been delighted with the outcome and we have never questioned our decision.
I'm sure you've been told this by your Vet, but Lymphoma is not painful.
Good luck.
Let me know if you need any other info.