Lighting – How to connect the LED strip lights

Not a complete answer, but here's some more info.

Brightness

While there are ways to calculate this that aren't that complicated, it requires knowing many coefficients that are not readily available, so ends up being an educated guess at best. You can do just as well totaling your current lighting's lumen output, then adjusting for changes in fixture styles. (I consider even a simple LED strip a "fixture" for the sake of this discussion) It's a starting point. If you use proper task lighting, there's a lot of room for variance in total levels.

Uneven light

You do not want to see the actual LED elements, it's really annoying. Besides diffusers, indirect lighting techniques work well, though require more lumens due to losses through reflection.

Positioning

I'm not sure what the issue is with parallel surfaces. The efficiency is mostly inherent in the fixture's ability to direct light where it's needed. The mounting surface has little to do with this, you need to direct the light where it's needed.

White Light

The "whiteness" is measured in degrees Kelvin. The temperature a black body must be heated to emit the same color of light. Standard daylight is often taken to be 6500K, anywhere in the 5000-7000 range is close enough for most tasks. You eyes adapt quickly to small variances. In residential settings, daylight is considered too harsh because we are so accustomed to incandescent lighting, so most home lighting is produced to output more in the 2000-3000K range to mimic the orange incandescent lighting.

Noise

How audible the noise is varies by manufacture and environment, as well as personal temperament. I don't think noise data is readily available. Testing in a noisy store will not yield any useful data, other than if you can hear it from a few feet away it is too loud. Noise can be attenuated by placing it in an enclosure, but keep in mind power supplies generate heat that has to be removed by ventilation, you cannot seal it into a sound proof box.

Try to place power supplies as far from your pillow as possible, trying to sleep is when it will be most bothersome. Placing it lower so there is likely to be more furnishings obstructing a direct path will help, as well as being surrounded by soft materials that do not reflect sound as well.

Past few weeks I have really come to appreciate the benefits of cable pull string. A nylon string used to help pull cables. You can drill the holes in the walls, cover them up and then when you get your cable, tie and tape it on one end, then pull from the other. Just make sure you make the holes big enough to pass the flat ribbon RGBW cable through along with the knots.

If you don't have cable pull string, you can get it at most hardware stores and the big box stores. You can also just use any strong string or twine you have. If you have UTP cable you can put that in temporarily then use it as a pull cord but it's not as strong as the pull string. That shouldn't be a problem for a small run like you're describing if it doesn't have a lot of sharp bends.

The problem with running UTP is that it's normally 24 gauge and even though it might just be a temporary fix, temporary can sometimes be a very long time as long as everything appears to be working and you have other things to do. So it's thinner than the usually 22 gauge RGBW cable conductors. According to this table on wire properties 22 gauge wire can handle up to 0.92 amps for power transmission and 24 gauge wire only 0.577 amps. If you know how many amps your light setup will use then you can make a safe decision.

When you have to use a different wire it's better to go with a larger size than a smaller size. You can get 5 conductor thermostat wire most places and that's generally 18 gauge. 18 gauge wire can handle up to 2.9 amps for power transmission so it's the safer choice.

I would personally just make the holes, pass some string, leaving plenty on each end to tie and grab, then install the cable when you get it.