I'm thinking you didn't mean to mention F lyrata as a bonsai candidate due to the large leaf size.
I have several of the species plant F benjamina, a forest of F benjamina "Variegata", and a number of F benjamina "Too Little", as well as a number of F microcarpa, F deltoidea, several F salicifolia/nerifolia, F nitida, and probably at lease a couple of others I'm missing at the moment. There is very little difference in the cultural wants of the genus - all my trees are in full sun all summer and under lights in winter. None of the species tolerate wet feet well, so avoid advice to "water when the top inch or two of the soil is dry" or anything similar. What's important is how moist the soil is deep in the pot, and this can be determined by using a "tell". Trees don't dip their roots in water and sip it up, they absorb water as vapor from the pores between soil particles or a molecule at a time from the microscopically thin layer of water that coats soil particles in damp or moist soils. Any water that collects between soil particles to form a saturated layer of soil near the pot's bottom will always be a limiting factor and soils that support this perched water table should be avoided to the greatest degree possible - especially those growing in shallow pots. For soil moisture, the operative words are moist or damp, never wet or soggy.
I highly recommend Foliage-Pro 9-3-6 as your 'go to' fertilizer for potted trees and houseplants. It has all nutrients essential to normal growth and doesn't derive any of its N from urea. Nitrate sources of N are easier on the plant, far less likely to cause ammonium toxicity when soils are overly hot or cool, or waterlogged. Ammonium toxicity in containerized plants is a rather common problem though it usually doesn't get diagnosed or is diagnosed as another issue altogether.
Using a 'tell'
Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need plenty of air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support the kind of root health most growers would like to see; and, a healthy root system is a prerequisite to a healthy plant.
Watering in small sips leads to avoid over-watering leads to a residual build-up of dissolved solids (salts) in the soil from tapwater and fertilizer solutions, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor.
In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.
Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.
One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16" (75-85mm) would work better. They usually come 48" (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.
Al
That little Weeping Fig (Ficus benjamina 'Variegata') has a nice root system started! I hope you will keep us updated on how your Bonsai experiment goes! I tried Bonsai once years ago when I was young, I don't recall what little tree it was that I used but it was fun pruning and wiring the branches.
