Yes, I take only 1 or 2 provinces of Ming at each war usually, except two of them where I carved a path inside Ming to reach new tributaries. On one hand I don't plan a WC, on the other hand, remember that at each war Ming is just an ally of the defender so its province are worth twice the usual cost in WS and DIP, and at almost each war I will take provinces from the attacked tributary.
Yes, razing is a very useful tool for horde. It gives you many MP points (20 for each razed point, and you raze 1 in any category if size is above 1 and another 1 for each 5 points in this category), some money (not much as your armies probably already looted the province, and also horde unity (the equivalent of legitimacy for the hordes. 100 horde unity = +5% discipline and -2 unrest). The MP points gained are reduced by 1 for each mil tech above 8, and eventually will turn negative in end game for MIL tech 29 or above, but at least to this date razing is still interesting for one other reason: it reduces the size of the province and so its coring cost.
The main idea in my own opinion when you conquer an area is to ask if you want to state it some day or not. If not, raze it and either raise automony to 100% to decrease unrest (before absolutism turns in) or give it to a vassal, or sell it to a tributary.
By the way the tributary mechanism is also useful as a horde, especially when you have close to 100% OE. Take states as tributaries and they will probably not be attacked, continue to conquer around them, isolating them, then in the last century stop the tribute and conquer them when you have the time. In the meantime they will still give you a lot of MP, money or manpower depending of what you need.
As for changing strategy, it is hard to remain a steppe all the way to the end of a WC as horde unity will decrease monthly faster as you grow while razing gives you less MP. Still with constant warfare and razing I was able to maintain it to the end.
I also started as Great Horde->Golden Horde, and was allied to the Ottos for a long time, then punching all other powers in the area (to be sure they don't grow, especially Muscovy into Russia or Timurids into Mughals). I waited to be over size 1000 before having a frontier with Ming whose mandate quickly fell. One big advantage Great Horde has over other hordes is that its capital starts in Europe and so you can created trade companies everywhere. By the way you can roughly ignore Western Europe and America until 1700.
