Yes, excellent timing for a standard and important beginner question!
Yes, 5ppm will more than prepare you for a full bioload, but whether or not you take advantage of it is totally up to completely different considerations! You see, the process of creating your "stocking plan" will lead you to a determination of the first stocking. It will all depend on which specific species end up in your plan.
Let's take an extreme example: If you were doing the rather rare thing of creating what we call a "species" tank, where the whole tank, water chemistry and aquascape would be devoted to a single species of fish and you were only introducing that type of fish and no other ones, and that species was of the type considered to be hardy enough to go into a new tank directly after the fishless cycle, then yes indeed, you would go ahead and do a full stocking, BOOM!
Or perhaps you were only doing 2 or 3 species and all of those happened to be extremely hardy and cheap.. well then they might all go right in too!
But in practice, what -really- happens 95% of the time is that most beginners are planning to create a "community" tank with quite a number of types that they've seen and like and which were what originally made them want a fish tank in the first place. Out of those, its very common to have one or two species that are either too delicate or for which one is going to have to pay a lot of money and so one wants/needs to hold off on those until the tank is still -more- mature!
The absolutely classic example of this are beginners wanting cardinal/neon tetra shoals. These fish are strange in that lots and lots of aquarists have observed that somehow they just have a much higher chance of living if they are introduced into a "6 month old" tank rather than a newly cycled tank. And that's -even if- the tank was well-cycled! So often a place is reserved for the neon shoal and not all fish are stocked immediately. The other example that's classic are "centerpiece" fish like angels or various cichlids and rams, some of which are either delicate or expensive or both. Its considered good practice in a lot of these cases to simply wait 6 months or so on these too, just to raise your statistical chances a bit too. Of course, one must recognize that there's plenty of variation about this depending on species and the individual situations people are in, not to mention opinions!
And just to make sure I didn't skip a basic part of your question: Yes, the large robust colonies of bacteria you've built up by the end of a good fishless cycling regimen will indeed "drop down" within a few days or weeks, to match whatever ammonia bioload they are presented with. BUT, that's of course exactly what you want in that you would always want your bacterial colonies to be too large at first. If they were too small then you'd just be back to a fish-in situation, which was what you were trying to avoid to begin with. So once you've switched to fish and done your first, hopefully pretty big, stocking, from then on you will have to observe the normal rules of only ever adding a small number of additional fish at a time. (I tend to think 2 or 3 smallish fish at a time but the experienced aquarists here may want to correct that or give a better guideline!)
~~waterdrop~~
