Jorge, reasonable questions, but don't worry so much. Yes, tubes sound better after they warm up and settle down for a half hour or so, but they work fine after about 30 seconds, and it will not harm them. Some gear has a "soft turn-on circuit" which brings them up gradually, which extends tube life, but if it doesn't have this circuitry, they are good to go quickly. Yes, chinese tubes tend to be not quite as quiet as expensive NOS, but they will still be adequate, unless you have astounding gear or very sensitive ears. New tubes seem to be improving in some cases, Shuguang Golden Treasure, Psvanne, and Genelex Gold Lion remakes are pretty good tubes. Yes, there can be a little hiss between songs if the volume is very high and your room is extremely quiet, but most people are not bothered by it. People who are bothered too much by "tube rush" get solid state gear and tolerate a different set of limitations. This may be an oversimplification, but it tends to matter most if you listen to classical symphonic music a lot, which has huge dynamics (so you may notice the hiss during very quiet passages.) If you listen mostly to rock and pop, you will rarely be bothered by tube noise. You do have to match the preamp and amp, as a mismatch can exacerbate the tube noise issue. To some extent, more expensive gear may be quieter, but that is not necessarily because of the tubes. Some of this stuff, all you can do is try it, and gradually, you will refine your own preferences.
