What would be the best dimensions and I guess overall way to go about my task? Currently using gimp. Do you recommend any websites I should check out. By the way I am very new at this but learning quick.
I don't think this is purely about dimensions and packages. This is about the whole design process from conception to final production, and, I suspect, is really beyond the scope of this site.
An important question at this point is: how much are you being paid to design this one label? That question will determine how much time you invest in the further stages of your design.
You're going to have to know what your label is being attached to. Is it, in fact, a bottle? Could it be a bottle, demijohn or carafe? What material is the item made from - ceramics, glass, plastic? What shape is the object? What quality is the product? Where was it made? Is there any distinct flavour or colour to the vodka?
So many questions, even before you start. Research is everything, from there you can start to look at the label itself. Research existing labels, particularly those that are popular or, if the product is being aimed at a particular demographic, then research that aspect. You need to get some info from the manufacturer about what they're looking for.
Once you've got all of your knowledge sorted, then you can start on your designs.
Really, this answer then feeds into @GerardFalla's answer.
I'm not sure I would stick to just vector tools, though. I would recommend paying the subscription price and going for a combination of Illustrator and Photoshop, though I know it's expensive (but that's where your costings come into it - you should be billing the client).
Personally, I feel this question is too broad.
You can accomplish a lot of what you need to do in Gimp, but I think it'll be far less effective than a dedicated vector design app.
Bottle label design has a fair amount of variability, both in size and in material typology - you might use a foil based label for a metallic look, a coated paperstock for a gloss look, or even a heavy matte paperstock or thin cardstock for a textured, raw paper look.
You can plan on a simple rectilinear design for the label's shape / profile, or you can do elaborate cutline design to get an interesting or æsthetically appropriate (depending upon the bottle's form) outline for the label - and some really expensive labels even do both cutline shapes and double-sided printing (which involves some seriously good registration) so that the back side of the label, seen through the bottle has some content or æsthetic styling.
I'd look at a range of bottles in a liquor shop, and I'd suggest both looking extensively at other vodka labels and looking at other non-vodka labels too, in order to get an idea of both the milieu in which your label will need to function and what's possible: remember you will want it to both exist comfortably in that milieu enough to want to feel as though it belongs there, and to stand out enough to grab someone's eye off the shelf absent any other stimulus.
In other words, the design, size and material need to display quality in terms of design and production such that it doesn't instantly read as cut-rate or gitchy.
If you've already identified the production house which will be producing your label (most bottlers will have a preferred vendor & spec) they may well be able to provide guidelines, or even a spec (or in some cases a design template file) which can help you with sizes - in many cases, there are typical or standard sizes in a given range, and then outside those can be done, but for considerably more money, so that's a calculus you'll need to understand and present to your client for decision-making pretty early in your design process.
I can tell you a typical outer size for a US wine label is 3.5" x 4", that most companies will also do squares up to 5" x 5", and that 4" x 6" is pretty common too.
Hope this helps some.
P.S. - worth mentioning that all of my answer is predicated upon you knowing something about your client's intent for the bottle form factor and overall design sensibility too - and that can vary to an amazing degree: these images here are all vodka bottles.