Well, I would go for something like a Yamaha or something from the Godin (said like Godan) line. Made in Canada, their instruments are high quality and don't cost much more than Yamaha. But you may not see or hear much of them if you live outside Canada. You can also try Alvarez, takamine. If this is the only guitar you want, and don't plan to buy a better guitar later when you get better then I would go with something close to the $500 mark.
You can try out a few different guitars at your local music store, and only go to a music store, not some big box store like best buy, even if they know what they are talking about.
Strings will come with the guitar when you buy it and you may want to buy one from the back room that isn't on the store floor, as many people could have played it, and scratched it. Though if you buy a model off the floor and its in decent condition they might give a discount, and an even bigger one if you see flaws or scratches in the lacquer.
For neck sizes, in terms of length, you won't find much difference. In terms or th shape of the back of the neck where your thumb rests, these can differ in size and shape, some are basically a radius if a circle, some are kind of half of an oval, some are far some are skinny. Though the cheaper acoustics will be generally the same.
Strings can be left on for a fairly long time depending on how much you play and how good you get, but your first set should last a decent amount of time. When you replace them I would go for D'Addario, or ernie ball acoustic bronze strings. They do go higher and lower in size, when you buy the first guitar I believe most acoustic guitars are strung with sizes 10-45 or maybe a bit bigger. The 10-45 will likely be referred to as 10's, and are usually light or medium guage. but this is all a bit technical.
I work ast a music store, and I check hundreds of guitars a week as they come into the store. I can help you with a lot of thing. If you need help changing strings I can help you with that, maybe you could send pics of the guitar and I can show you how to do it properly. Plus here areany videos online