yes on the mL.
If his numbers are about 350 or lower....
the vial may be more than you need for now. Lantus is also available in pens. There are pharmacies that will break up a 5 pack.
You don't use the pen as intended , but you use it like a vial. It has a rubber stopper where you can stick the needle in and draw out insulin.
Most of us don't dose a cat in whole units, the dose changes and the pen ( with the needles that are optional) doesn't do half or quarter unit measurements.
Many vets will go from 1 unit to 2 units for an increase and that can be too too much for a tiny creature like a cat.
We increase in 0.25u when needed. This is so you don't miss the optimum dose.
I see that food you listed is a dry food. Now that he is diabetic, the better diet for him would be canned.
And all the instinct canned foods are really good for him. I used to say if I could get my cat to eat that all the time, I would pick that one.
If you can afford that one, good choice.
I myself like to have a small repertoire because I find that food companies suddenly change formulas and phase out the ones I like.

Here is our latest food guide
http://catinfo.org/docs/CatFoodProteinFatCarbPhosphorusChart.pdf
you want to pick canned foods that are less than 10% but also have a few cans that are a higher carb for boosting his numbers should he go too low.
Just about any of the gravy foods will do that.
The reason for canned food is at
http://catinfo.org/
However, there are some cats that are just dry food addicts and it takes a while to convert them. We have all kinds of tips for that.
The other good possibility is freeze dried cat food , often raw.
The other two brands I really like for quality are Wild Calling ( they have rabbit) and Tiki Cat ( I only get the chicken varieties )
Fancy feast is the most common one because it's easily available and under $1 a can.
The problem with fancyfeast is they are pretty high in phosphorus which can be bad if your cat develops CKD.
Dr. Pierson is the one who wrote the nutrition guideline.
Most vets seem to only get a few hours on diet and nutrition which is why so many of them sell the prescription stuff, especially Hill's.
It's a partnership that Hill's gives away so many scholarships and vets don't seem to question the products.
We do.
The other thing you want to explore is freeze dried cat treats. ( and they have rabbit for that too -
https://www.amazon.com/Vital-Essentials-Freeze-Dried-Rabbit-Treats/dp/B01B77ZACW/ref=sr_1_4?ie=UTF8&qid=1495871768&sr=8-4&keywords=freeze+dried+rabbit
look around dog treats come in bigger bags and are usually just the same, just a better deal.
another good one is
whole life turkey
or the fresh is best brand.
I don't know what protein you are trying to avoid. I am assuming chicken.