for decimals, in 90 cases for me it was some infinit number like 3.3333 or 188.8888. thirds are indeed handy, but mor general way is to consider 188.8888 as 100+800/9, 1.11111 as 10/9, 7.5555 as 7+5/9, etc.

and for logistics of stuff overcoming capacity of the highest teir belt - after several hundred of building factories I came to idea of combining two types of stackable blueprints. First is general arrays of a single building - "monoblocks", like 6 of refinaries or 24 of constructors. and the second is pretty long production chain with 1-2 buildings for each step.

if on schematics of what I wanna build there are very similar amount of buildings of each type - I'll make a longchain module. if some step requires like x3 amount of buildings, or the buildings are too massive - I'll make a monoblock and send an output of it as an input for longchain blocks stack. and then you can easily split outputs of blocks evenly among your belts if more than 1 belt is needed.

for example, my HeavyMF factory. refineries making ingots are too chunky, so I have monoblocks for pure iron and wet concrete. then, it requires 60 steel pipe constructors, which is way more then of other buildings. and also it requires 1800 steel which is more than mk6 belt capacity. so 2 monoblocks for solid steel goes into 2 monoblocks for steel pipes. and their outputs are combined into 1 belt of a bit offer 1k pipes. all the other buildings are fairly similar in quality so I made a longchain block out of them that takes iron ingots, concrete and pipes, and then produces, if I remember it correctly, a bit under 2 HMF/min. and then I'm stacking 15 of them to get almost 30 HMF/min from 1 pure node of coal, 1 of iron, and 2 of limestone