Perhaps I have misunderstood the OP's requirements?
But your code should work with:

#$mw->maxsize(1000,1200);
#$mw->minsize(400,300);
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If I understood correctly, the idea is to size the window so that all data can be shown without scrollbars, if possible.

Update: Your code is interesting. I'm not sure either one of us really understands the OP's requirement.

Update2: Now that I look at your code vs mine... The main difference is that I use pack() instead of grid(). With weird shaped GUI regions, pack() tends to work better as long as you are using enough frames. In general with more than one object, you put them into a Frame and than pack that frame into a frame. Grid() is different and I haven't used it. But this can work well if every row is the "same" (i.e., lining up the columns).

The main thing appears to be that the OP will need to calculate desired width size and then use that value to configure the window.