Yes, there is a hole in your plan. As the replies above indicate, not only is separating the juvenile shrimp from the adults unnecessary, it would be very difficult, if not impossible. In my opinion you're making this too difficult. Don't divide the tank. That will cut down on the equipment you need, and make it more visually appealing.
Below is some information I've put together with basic information on keeping shrimp that you might find useful.
Neocaridina shrimp (Neocaridina davidi; red cherry shrimp and the other available colors) are one of the easiest ornamental shrimp to keep, with a wider range of suitable water parameters than caridinas. Their parameters do overlap, but it's a narrow range, and not something I'd recommend for inexperienced shrimp keepers. I don't have any experience with caridinas (at least not yet), so I won't address them here.
6.8 to 8.0 pH is usually the recommended range for neos, with Gh from 6-12 and Kh at least 4. There are supplements you can add to the water to raise the hardness if yours is low. They will tolerate a wide range of temperatures, but around 72° F is generally considered best. At higher temperatures they will grow faster and breed faster, but they will also not live as long. Basically, higher temperatures accelerate their lifespan. Shrimp are sensitive to copper in the water, though the small amounts in commercial fish and shrimp food won't hurt them.
If you’re curious about how many to start with, the answer is as many as you can afford, but if money is a factor (which it often is for most of us), you can get a nice colony going with 10 or so. Of course, it will take longer than if you start with 25, but you’ll still probably get to 100 sooner than you expect.
There are many color varieties, and they will readily breed with each other. The results will generally be brown or clear after a few generations. For this reason, if you want to maintain a specific color it's best not to mix them. Even if you do stick with a single color you'll need to remove undesirable colors occasionally. The amount of culling you'll need to do will likely vary depending on the purity of the shrimp you start with. From my personal experience my red shrimp need a fair bit of culling, while the blues ones need very little. Many people do keep and enjoy mixed colors, and there's certainly nothing wrong with that. If you do cull, you can have a separate dedicated tank for them, or add them to tanks with fish. Even in tanks with dedicated shrimp hunters you'd be surprised how many will survive, especially given adequate hiding places. I occasionally see one in my 65 gallon tank, and my big angelfish just loves shrimp.
To get the most enjoyment from shrimp, keep them in shrimp only tanks, or just shrimp and snails. You don't have to worry about predation, and they'll also be more visible if there aren't predators in the tank with them, even if the predators are too small to be a threat to adult shrimp.
Even if they are the only things in the tank, they will feel more secure with hiding places, especially when molting or when a female is releasing babies. Dense plants are a good option. Java moss, guppy grass, Süßwassertang, and pearl weed are some good choices. A pile of rocks, sized so that the shrimp can crawl inside, is also a good idea.
They are sensitive to changing water parameters, so most experienced shrimp keepers recommend limiting water changes to around 15%, and the new water should be close to the same temperature. If you do larger water changes, it’s even more important to temperature match the water.
Since they need biofilm to graze on, and are very intolerant of ammonia and nitrites, it's usually recommended to let a tank run for at least 3 months before adding shrimp, and 4 months is better. You might get by with adding them sooner by adding a sponge filter, plants, substrate, etc. from an established tank, but you still aren't likely to have as much success as you will if you're patient and let the tank "season" (I know this from first-hand experience).
In addition to the biofilm, they will also benefit from being fed. There are several commercial foods especially for shrimp, but I've also given mine several kinds of fish food, and they've eaten all of them. While there are mixed opinions about it, many people believe they also benefit from blanched vegetables once or twice a week. I've tried several things, and mine seem to prefer zucchini and spinach, followed by sweet peppers. I usually feed those late in the evening and remove any uneaten portion the next morning. By the way, shrimp just LOOOVE freshly crushed snails. Mine will swarm all over one.
If you use CO2 in shrimp tanks keep it around 10 – 15 ppm, and definitely below 20 ppm. They often can’t tolerate the pH swings and/or elevated CO2 levels at higher concentrations.
Of course, if you want to establish a colony you need males and females. Females are usually larger, and have better color, so when selecting them in a store you can get all females if you aren’t careful. It’s not difficult to tell them apart, even on shrimp that are the same size. The abdomen (the rear half) of females is larger than males, with the bottom line sagging down. Males’ abdomen is thinner, and it’s pretty much a straight taper from front to back.
As they reach maturity, females will develop a “saddle” on their back. This saddle (usually yellow) is the unfertilized eggs showing through their shell. They're ready to breed when they next molt, after which the fertilized eggs will move down below their abdomen where she will constantly “fan” them and juggle them around with their swimmerets to keep them aerated. Unlike some shrimp, neos don't have a larval stage, so they’ll hatch as fully developed, but very small, shrimp after about 4 weeks.
If you suddenly notice the shrimp swimming around the tank more than usual, it’s probably nothing to worry about. When a saddled female molts she releases pheromones signaling she’s ready to have her eggs fertilized, which gets the males swimming around trying to find her.
If you notice a shrimp with a lighter colored lateral line on top, that's called a "racing stripe", and is a harmless feature that's common with some color varieties. It will typically get wider, with the edges more ragged, as the shrimp gets older.
You won't likely need to worry about a shrimp becoming overstocked. A well planted 10 gallon tank can literally hold hundreds of shrimp without being crowded.