[Beatris]

Why did Ibn Taymiyah praise some Sufis? Why were so many scholars of the past - the same ones who would say Qaala Allah and Qaala Rasoolullah - ahl-e-tasawwuf?

Because some Sufis were within the bounds of the shari'ah and some who attributed themselves to Sufism were shameless zanadiqah, and there were some who were in-between this and fell somewhat into innovations and problematic things while remaining essentially correct-minded. Ibn Taymiyyah has a famous fatwa on the three groups of sufis which you can probably find with a quick google that quite amply sums up his considerations on them.

Of course, his word is not final- it is a hardly contested fact that Imam Ahmad ordered the boycott of early ascetics which Ibn Taymiyyah admired, such as al-Harith al-Muhasibi- I believe you can read an article to that effect on asharis.wordpress, wherever you can find the biography of his. The article accuses the early muhaddithin of 'intolerance-' ha!

As for your second question, is it ahl-e-tasawwuf the way you define it, the way Ibn Taymiyyah defined it, or the way Ahmed Raza Khan Barelwi defined it? For the former, I haven't the slightest what your borders are, for the second, because everyone has faults and also good points and we should pick on the good points while not overlooking the faults- if they are there, and if it is the third, then nobody who defined tasawwuf the way the heretic Raza Khan did would be a great scholar of anything- aside perhaps from a how-to guide on bid'ah and heresy.