Hi and welcome to our family of friends here at the User Group. Dogs are actually great at coping with SubQ fluids ... but owners rarely are, and it's the anxiety of owners that transfers to a dog. So, the answer here is to make sure you stay relaxed and calm when preparing for and giving the fluids. Make it a routine, just like any other task you might perform during the day or evening. If blood numbers start improving, talk to your vet about giving once a day or even every alternate day.
I'm curious about the blood results you might have. Can you post the last set of results for me please. If you don't have them, please ask your vet for a copy. Also, do you know if an SDM<A test was undertaken? Also, have you had a urinalysis done for specific gravity and protein leakage? And, did your vet undertake a blood pressure check?
I can answer some of your other questions and concerns after I have access to the blood numbers.
When the vet diagnosed kidney disease, did he/she suggest the stage the disease has reached? This impacts on the type of foods being given.
How long can a dog last with kidney disease is impossible to answer. Every dog is different and so much depends on how much damage has been caused to the kidneys. While early diagnosis, good management and prompt diet changes all help prolong life and improve quality of life, the disease can only ever be stalled and will eventually continue to impact on health. I have known dogs survive for 2 years, but there are those that decline rapidly and don't even survive a few days. As I said, every dog and every case of this dreadful disease is different.
I am including a link to one of my articles below, which is a good starting point on the learning curve. Let me know once you have read it and ask any questions you may have, then I will send you a link to another one that I think will prove helpful.