I suggest to start small with three primes or 2 primes + 1 zoom and go from there. Keep your kit's lens to explore on 18-55. I had my K100D for about a year and LBA has costed me buying a lot of lens and hence less time for the passion in photo taking. Once you get a good prime, you will use less on zoom but you may still want to have a zoom to cover a useful range for convenience.
You hear many people going after the trio with something like the limited in 21mm/43mm/70mm or 77mm.. But those are way out of my budget for hobby. And I find the cheap quality gear to make up my own trio. And you already have your 50mm f/1.7, please hold yourself from buying another 50mm and stick with what you have, the f/1.7 is a good one and in general f/2.0 is plenty even for night time shooting.
I have my cheapo trio costing a small fraction with the ultimate trio in limited lens. I get what I paid for but I am just as satisfied with cheaper gear and learn to concur the obstacles in the pitfalls of cheaper gear. Nothing beats the joy of shooting great pictures with inexpensive gear. But the opposite is also true, it sucks life when you swear on your gear.
I don't recommend my Spiratone 20mm f/2.8 as yet as I am not satisfied on the sharpness and color. And I have other not-so-wide fixed prime to recommend.
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Wider end:
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50mm is covered
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I like my
FA 50 f/1.4 for the AF with my boys
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mid-tele (zoom)
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I recommend a zoom instead of a prime as the 70/77/85 are all expensive unless you don't mind something that is hard to use like my Jupiter9 85mm f.2.0.
I recommend these few zooms to study based on your budget
If you are willing to go with manual focus gear, you have a lot of options. But be extremely picky on your purchase.