Hey there. I see you're a little confused, so I'll try and share my 2c worth of information.
Don't get into this assumption that bigger is better, larger aperture, longer tele, wider wide, longer zoom, etc. Each lens was designed to its own purpose, and few others really beat it at that. You can't judge a lens purely by numbers (or a camera, for that matter).
That being said, you won't be able to find all focal lengths you're looking for with an f/1.2 aperture (actually you could, but not for 35mm film/APS-C digital, those are CCTV lenses). Aperture is actually the focal length of a lens assembly divided by its diameter at its optical center. Being a multiple of focal length, and transmittance not being dependant on it, aperture is noted as "f/#". Aperture(f) stops commonly run from 1, and go by multiplying with the square root of 2 (approx. 1.4) - hence the series 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 etc. The reason is the definition of an f-stop difference as the light required to double the light captured. You could a) halve shutter speed, b) double film/sensor sensitivity, c) double lens area. We will concentrate on alternative c, although a) and b) are sometimes more practical. Doubling lens area means multiplying radius by 1.4 (think A = pi * r^2). As I said, finding all your favorite focal lengths in a nice, big aperture isn't always possible, because, let's say you need a f/2 300mm telephoto lens. That means you need a lens that has glass 15cm in diameter, and I'm not even talking about the barrel. However, a vast majority of lenses float around the same aperture value, so I'll mention some of these values so you have a reference when shopping around. I'll only be talking prime lenses, because that's what I use and what I think gets best results for least money.
- 24mm and wider - things can get expensive, so I'd rather buy a 28mm and wait for a full-frame to get really wide images from it. In this wide section, every mm counts.
- 28mm - f/2.8 is the norm, though f/3.5 is also OK. Finding faster usually commands for more money.
- 35mm - here it depends. You'll see some 35mm lenses have "just" f/3.5, the norm is again f/2.8. Lenses covering full 35mm format usually stop at f/2.8, but there were also expensive ones that went to f/2. Now, 35mm is a popular focal length for APS-C DSLRs (it isn't wide anymore), it kind of tends to replace the 50mm focal length. You will see 35mm f/1.4, but those only cover this smaller frame for digital, because lenses with smaller image circles are easier to produce.
- 50mm - the most common focal length you'll find on film bodies. Looking through them, you'll quickly understand why - normal perspective. f/2 is COMMON (I certainly wouldn't buy a 50mm lens slower than f/2, if only there would be something special about it, like macro or small like the Industar 50-2). f/1.8 or 1.7 is fine, in my experience you don't NEED f/1.4 or f/1.2, you just want it.
- 80-85mm - this is the "portrait" focal length. I tried to skip these, because they're expensive. f/2 is the norm here, faster than that is very sought after.
- 135mm - the most common telephoto lens in the film era. It's actually a short telephoto, if you think you're going to spy your neighbours with this. f/2.8 is the norm, f/3.5 is also common; faster than f/2.8 is going to get you some HUGE glass (and some serious weight lifting), which can also be difficult to control in terms of optical performance (prone to flare, chromatic abberation, softness, etc). Not recommended. The focal length itself is nice and I personally recommend getting one of these for portraits.
- 200mm - f/4 is the norm, these are a little slower and bigger, thus harder to shoot handheld (require more light, and are more sensitive to shake). f/2.8 is considered FAST among these lands, I think f/2 is unheard of.
- 300mm and above - I have no clue myself, because these are impractical for my style of shooting - would require a tripod.
Also, something you'll surely have to deal with later, although now is kind of theoretical. Depth of field increases with (the square of?) the distance at which the lens is focused. being virtually infinite at infinity. This has two important consequences. First, this is exactly what makes macro photography difficult. Secondly, it means you can't get a nice, clean shot with blurry background with your subject at any distance from you. That's why all "bokeh" shots are close-ups.
In a nutshell, as long as you get a K-mount lens and it fits the above criteria, you should be good to go. Don't spend a fortune on super-fast glass, you'll soon find that you don't use it wide open that often. Sorry for the long post, I tried to be helpful, but it seems I got beyond myself