OK, there are lots of things going on here
1) Yup, we'll bump up the dialog size. The Mac gave you four characters, but regardless, its too small.
1b) We've had other requests for this, so we'll definitely be doing it in the future. I doubt it will make it into the 10.3.1 bug fix release, but its on our list.
2) This is an interesting one. Technically, its working correctly, but differently from what you expect. The [COUNT] command means to give you the number of lemmas (or inflected words, or tag combinations) that occur x-y number of times. What you said in your construct is "Give me the number of Lemmas that occur > 2000 times, that are also Nouns." 'lo' matches this criteria - it occurs well over 2000 times, but only 4 of those hits are Nouns (the rest are Particles). It seems like you are trying to search instead for "Give me the number of Nouns that occur over 2000 times", which is a totally different way of doing or thinking about COUNT. The easiest way to do this is simply a [NOUN] search, then looking at analysis to grab the words over a specific number of hits. Or, use your search, but be aware of the subtle difference of the results.
Its an interesting question! We've had COUNT for years, and none of us could recall a time when someone was blocked by this particular nature of the feature, until now