I work on a variety of figure scales, from 5mm to 1/35, 1/48, 1/16, 1/3 and so on. I use the same sized brushes for everything. The only difference is how large the scale is. If I am base coating a large figure like 1/3, I use a 2940 or a 1395. Again, that's just for base coating. From there I move to either a 3000 round or a 3000-1 round. If I am base coating 1/16 or smaller, I usually start with the 3000 round. I'll even do a lot of blending with those too. If I need to go finer detail, I use either a 7500 10/0 or on down to a 7000. Realistically though, the 7000 is only ever used for outlining and eyes. Look at this figure here:
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I used to use real small brushes like the 7500 exclusively, but have since "grown up" so to speak and have way more control over what I am painting. I have had people tell me that my brush painting and blending looks as good as an airbrush work, which I am proud of. If you have any other questions I might help you with just ask me.
JigSawMan