Glad to hear that you are well on your way to achieving coffee nirvana. Just wondering though, what type of grinder are you using?
With some grinders used from new, the new burrs may seat in a little with the first few grinds giving the impression that under-extraction is taking place when in fact, the grind is gradually getting a little bit coarser each time you grind. If your grinder is of a type that uses a single nut to secure the rotating burr, this nut will tighten down a small amount until a sort of equalibrium is reached.
Its a bit unusual for coffee beans to go stale after only four or five days, unless the method of storage leaves a bit to be desired. I keep newly roasted beans in black plastic one-way valve zip-lock bags until Im ready to use them and then store in a clean air-tight container. These are in turn stored in a cupboard that is away from outside walls of the house and therefore much more temperature stable. Ive found that my roasted beans remain fresh to the taste for two weeks or more when stored this way but most often they are completely depleted within a week or so.
Keep up the good work with Silvia. All the best,