One of the benefits / purposes of fishless cycling is the ability to heavily stock your tank right away. By cycling it at 4ppm of ammonia, you are conditioning the bio-filter to handle a tank full of fish.
How many to add at first comes down to knowing your fish. If it's a community tank of small, peaceful schooling fish I wouldn't be hesitant to stock them all. Not only will the fish not produce 4ppm of ammonia in a day (unless it is ridiculously overstocked), but they also produce a small, steady stream of ammonia as opposed to a person dropping 4ppm in all at once out of a bottle. So the toxins are steadily converted instead of asking the bacteria to swallow it all at once.
When it gets complicated is when you're dealing with the territorial, aggressive species who may need time to set up their territories and hierarchy. That's when research is key about the order in which to add them.
It's really personal preference how fast or slow you add them, but the bacteria will adjust to the bio-load (# of fish in the tank), so if some time has passed since the last additions, you'll want to add lightly and slowly.
Also, the inch per gallon "rule" is something to completely ignore. It's one of those guidelines pet stores give out which is total garbage. That's how things like Oscars in a 20 gallon tank happen. The best thing to do would be research the fish you're interested in, and feel free to start threads about your proposed stock list for other members to take a peek at. There's lots of experienced keepers here who are happy to help
