Welcome to the forums, and congratulations on your incoming K-70!
Regarding UV filters... Some time back, I was a big fan of them for protecting my lenses. Many folks here told me they degraded image quality, and for a time I was adamant that they didn't. In many of my photos, they
definitely didn't - at least, not that I could notice, and I'm picky. And then, I found that in
some photos - just as my friends here warned me - they
did affect IQ... and those photos were more-or-less ruined (compromised at the very least). If you have strong light sources in your scene - the sun, street lights, car headlights etc. - you can get flare and reflections that wouldn't be there without the filter. Plus, the way the filters are constructed and coatings applied can introduce strange artefacts that I've found particularly noticeable at longer focal lengths. But, used sparingly as and when needed, they can be helpful, IMHO. If I'm shooting in good weather and in a location where natural debris such as grit or sand won't likely get onto my lens, I shoot without a UV filter attached. But, if I'm shooting at the beach, or on a wet and windy day where I might want to frequently dry off or clean the front of the lens without taking proper precautions, I fit a UV filter for protection (and accept that there may be some compromises in the captured image quality)... that way, I can use a microfibre cloth (or even my shirt tail
) to clean the front of the lens without worrying if there's something on it that could scratch the glass... and if it does, I'm only out the cost of a relatively cheap UV filter. I've had best results from Hoya HMC Slim UV filters...
As for other types... For most general shooting, you don't really
need any. But, a CPL (circular polarising) filter can be useful for removing reflections in glass and water, or emphasising blue skies, though it only works if you're shooting at certain angles to the light source, and isn't advised at wide angles due to inconsistent effect across the field of view. An ND filter can be useful too, if you wish to perform longer exposures on bright, sunny days - for example, if you want to create a smoother appearance to flowing water. Something like a 4 or 6 stop ND might be a good starting point.
As has already been suggested, cheap filters aren't a good idea. There's no point in sticking cheap, uncoated Chinese glass (or, worse still, plastic) in front of your nice, high performance lens. Your system is only as good as the weakest link in the chain. That said, you don't need to spend hundreds of dollars. Since I don't use filters that often, I'm happy to stick with relatively-low-cost major brands like Hoya, Marumi, Tiffen etc. If you're really getting into regular filter use, though, there are specialist brands that can be much better - but considerably pricier