Hello and welcome to FDMB!
I think everyone has a lot of the basic information covered very very well (everyone here is soooo helpful) so I just wanted to add some information about your questions about the B-12 based on my personal experiences (I am not an expert by any stretch of the imagination).
This is something that someone told me when I first joined and was inquiring about B-12, my concerns about my vets reaction to starting it, and etc:
You do NOT NEED your vets approval to start your cat on B-12. Period.
There are water soluable vitamins and fat soluable vitamins. Fat soluable vitamins are stored when there are excess and can become dangerous if they are taken more than being used. B-12 is a water soluable vitamin meaning anything that is not absorbed by your cat will be excreted.
Willy has neuropathy and had it for awhile but we didn‘t recognize it until after he was diagnosed and we started home testing (we do pad pricks) which is what really launched us into researching it.
When looking for B-12 you are looking at the form rather than what it’s actually named on the label. The form, Methyl-B12 or Methylcobalamin is what you’re looking for. This form of B-12 is absorbed into the spinal fluid, which is what makes it effective. Sometimes you can find normal “B-12” (instead of “Methyl-B12) and when you look at the label it’s in methyl form. This tends to run cheaper. What you do not want is the cyanocobalamin form, it won't hurt the kitty but it won't help either because it's not absorbed in the same way. You want to make sure that the pills are free of soy, wheat, etc. and as natural as possible because they will often contain flavors and sugar.
Unfortunately, we checked GNC, Walmart, Target, etc. and the “B-12” we found at these places was not in methyl form but we did find it at our local organic store that actually has a very large vitamin/herb area inside of it. The ones we found come in 1mg (1,000 mcg) pills. We give Willy 4 pills (4,000 mcg) a day. We split the dose into 2 pills and dissolve in water either by crushing them (I have found it easier to do this in water) up or by letting them dissolve for a few hours in water and then we mix the solution into his food.
Most of the b-12 you will find is flavored and contains a little bit of sugar because it's meant to be taken by people sublingually (under the tongue). This seems to be such a small amount of sugar that it doesn't affect Willy's BG (he is carb sensitive). As long as the flavoring is natural, that should be ok too. The only concern I was given is that some forms of sugar used to flavor medications for people are harmful to cats. I cannot recall what it is, specifically (hopefully someone can help with this), and I am having a hard time locating the post about it but the kind we buy is super natural/organic so it hasn't been an issue for us. It would be an issue if we ever had to buy online but luckily this store has several brands of "methyl-b12" and 1 or 2 brands that have regular b-12 in a methyl form. We pay around $9-11 for a jar of 150 pills.
As far as the results, Willy still is a little awkward sometimes. He had the neuropathy for a long time (at least 8 months) but he’s doing remarkably better now, so don't let anyone tell you it's too late to start! When we are unable to give the B-12 for a day or so, we notice a marked deterioration in his ability to move around effectively so I know it really is helping.
Finally, a little something about the vet. I think it is more important to find a vet that is teachable, respects your wants and your goals, and is willing to work with you for the treatment that YOU would like. My vet was very knowledgeable about FD in a general sense but her methods of treating it were, to be blunt, very dated. I joined this forum and joined the Lantus support group and I realized I wanted to treat Willy based on the protocol used there because it was effective and in-line with my goals.
I spent a lot of time learning about the process and doing research on this site and gathering home testing data on my spreadsheet. When I set up a meeting with my vet, I honestly thought that I was going to be looking for a new vet because our previous encounters with me disagreeing to advice didn't go over so well. I went in with the mindset that as a professional, she would be interested in learning about this protocol that I wanted to use because I was bringing her actual medical information and not just “I heard this on the internet“. (Vets have to know so much about so many things in so many species, FD is just one thing). I made sure to approach her respectfully, because she is a knowledgeable professional, but firmly, because Willy is MY cat (and I am the one paying for the service).
I discussed my spreadsheet with her and pointed out things about it that I thought we interesting or that she should know. I then CLEARLY explained what I wanted to happen (I want Willy in the range of 50-120, preferably hovering around 70). I knew she might not be comfortable with this range (it seems some vets feel FD cats BG should be closer to 200) so I showed/explained my Hypo treatment plan and a list of what was in my kit. I then showed her a chart and medical articles of the protocol that I wanted to follow and explained, because I was home testing, this is what I wanted to do to achieve my goal. She spent several minutes reading through it and seemed unsure but I offered her the link to Willy’s spreadsheet and told her she was welcome to check in with us at any time. She has supported my decision to treat Willy this way but I don’t think it would have worked out like this if I had not brought her the information I did and explained myself and my goals clearly.
Anyways, welcome again to FDMB! You will find so many helpful hands and so much support here it will boggle your mind maybe more so than all the information that is available! We hope to see you in the Lantus forum soon!
Stephanie&Willy
They will be my backups when I can't be there to do it. I have given him 2 shots a day since then and he's been the same way. It really seems like it doesn't bother him at all....YEAH! 
