grammar - Longest sentence yet (Text Analysis). How do we decompile this sentence?

> Context:
On the other hand, Italian writers did well to draw on the Tuscan vernacular rather than the other vernaculars of Italy [1250] for the reasons that everyone knows and which we have stated pp.1246, end-47, beginning.

But it would be silly, absurd, pedantic, and ridiculous to conclude from this that only that vernacular can therefore be drawn on, that writers can only write in the manner and to the extent that that particular people speaks, that the Italian language and Italian literature wholly depend on the common people of Tuscany (when it does not even depend on the common people at all, but simply uses them when it so chooses), that in and outside of Tuscany, an Italian writer cannot create words or phrases that the Tuscan populace does not use, that, in short, someone who is not Tuscan, indeed, who is not Florentine, or not actually from the Old Market, is not Italian.

The questions would be:

1.There are two 'that' in line 3, would someone kindly explain this queer using of 'that'?

2.Is it acceptable writing in English using 'that' so many times in a single sentence? Wouldn't it be more appropriate if for example the first and second line:
'But it would be silly, absurd, pedantic, and ridiculous to conclude that only vernacular can therefore be drawn on'

3.If we decompile those 'thats' into multiple sentences, would it change the conveyed meaning?

Thank you!