Very new to DSLR video

[Djpriddle]

Hi,
I'm very new to using DSLR as I've always shot on camcorders etc. but I recently purchased a Pentax K30 to expand my horizons a bit. I bought a number of lenses, and intend to get more but I'm unsure on the next steps. I have the kit 18-55 lens, and a tele 55-200? Which are great for photography, but the aperture is not big enough for any decent shooting so far. I found a second hand 2.8 105mm prime sigma lens which is much, much better.

Would you suggest prime over tele? I think the 105 is great for portrait style, but I need something wider.

how can I work out the focal length on DSLR? Is it x1.4? And why?

Sorry ti for all the questions, I'm just trying to get to grips with the techniques. I'm shooting some promo videos for my book, and I want to get the best results possible. This is what I have so far, but I need to do another. It's shot with the K30 and the prime lens, and with all of the contrast and saturation taken out on the camera. Then run through magic bullet, for the extra correction.

Any by advice would be gratefully received. Thanks in advance.