Stupid question, but why are floating plants a key to shrimp bowls?
Floating plants have huge nutrient/resource advantages (specifically access to atmosphere and the CO2 that it contains as well as more access to light).
Several of the most popular floating plants also happen to be prized for their nutrient hungry and rapid growth properties which makes them ideal 'nitrate suckers' which is why they are so important in a very small eco-system like a shrimp bowl. Not only are they key for soaking up all of the nutrients/chemicals/organics released by the Miracle Gro as the initial organic content is exposed to the tank water but they are also key long-term in 'filtering' out the nitrates that would otherwise poison and kill the shrimp in such a small water volume (without mechanical filtration).
I like floating plants like frogbit for algae control as well for two reasons. They block light from entering the tank which decreases the amount of light that the algae can use to grow and they suck up a lot of the nutrients that the algae is trying to use to grow.
In a shrimp bowl you are going to be relying on the plant mass to provide your filtration and relying on the bio-film associated with a mature planted environment to provide a secondary source of food for the shrimp. Floating plants are a great way to bridge the gap between your initial planting (when the aquascape still needs to grow in and mature) and the point where the bowl matures and becomes more naturally balanced in a chemical and biological sense (at which point you should be able to remove the floating plants if you really want to and still have enough plant mass to keep the water clean and hopefully to avoid algae outbreaks).
I would recommend any of the neocaridina species or color morphs (Red Cherry Shrimp, yellow neos, rilis, snowballs, blue pearls, etc.). In my heavily planted bowl I have trouble seeing the regular red cherry shrimp that I tossed in there (between the natural tannins in the water that I have yet to remove by doing water changes and the fact that my bowls are jungle thick with plants). I would think that something brighter like a yellow neo might be more striking visually but I have not put this to the test personally yet as I don't have any yellows.
You can have success with these Walstad style bowls in many different fashions and different styles but the easiest and safest way is to plant them heavily and just let the massive amount of nutrients and the initial boost from the decaying organics in the Miracle Gro work their magic. This initial nutrient rich environment will result in incredible growth for quite a while (more than long enough for your plants to fill in and for the bowl to mature) and I would say that no ferts are needed during this stage. None are really needed at all but at some point in the future you may decide to supplement the water column slightly with ferts.