Re cable and construction:
Ready-made cables are iffy at best. I have never seen published specifications on ready mades. Molded-on connectors are repair-proof.
Learn how to use a soldering gun or iron. Use good connectors and cable. Be careful, don't get in a rush, and your cables will be as good and reliable, if not more so, as any you can buy, and cheaper.
Learn how to check for continuity on a suspect cable. Somebody other than you will at some point be unplugging cables, and will be unconcerned or unaware of the time it takes to make and repair them. The problems are always at the connectors. In over 50 years of playing music and being in studios I have NEVER seen a failure any other place- (though it must surely be possible.)
In choosing cable, the better manufacturers- Canare, Mogami, Gotham, Belden, and others- publish specs on their offerings. Depending on grade, there is little difference between the better grades. In comparing, it will be necessary to do metric conversions. Impedance per foot indicates signal loss per foot, not necessarily linearly. Capacitance per foot indicates filtering per foot, starting at the highest frequencies. (Think of a long skinny crossover, or low-pass filter.) It is likely that there are roll-off and attenuation variations between brands, but considering the tiny capacitance per foot differences, it is difficult to imagine this outside the lab realm. Available ratings on this are typically found at less than 60 picofarads per foot. That's micro micro farads. On studio lengths, likely indiscernible without lab test gear.
Interestingly, Canare publishes a decibel loss of .9 per 1000 feet. If the typical studio cable is about 25 feet long, excluding rack, patch bay, console, and fixed runs, that signal loss in that cable is .0225 dB. My ears can't hear that at my age, and considering the logarithmic nature of the decibel, I doubt ears 50 years younger can either.
Some manufacturers also publish RF rejection data. I have never found this meaningful. Out side of particular problem locations (location live recording, for example) balanced Lo Z cables have never been a discernible source of RF interference in my experience.
Neumann, in literature for some of their mics, claim that cable runs up to 1000 ft. can be made without degradation of loss of signal. Granted, that may be dependent on mic output level and the cable they are using, but it sure seems to hint that "normal" ears couldn't tell the difference between a 15 ft cable and a 25 ft cable of the same type and brand using the same mic, and comparable signal, of course holding all other variables the same.