I've been thinking about it and the only problem is the bugs. Is there a lot of them? Oh and one more thing I don't know if this is a bug but when I got hearthfire I could do horse combat without "Dawnguard"

I rather enjoyed Dawnguard, it was a good ride, although I'm not quite sure it's worth the full price. Don't remember experiencing any bugs either, so there can't been anything major.

Didn't care much for Hearthfire though, for me that DLC was mainly about fast travelling between locations to buy supplies so you can build stuff. Very boring.

Mounted Combat was introduced in the 1.6 patch, not with Dawnguard or Hearthfire, so it's not surprising that you can do it

Get it but only when you are at sufficiently higher level to make the vampire attacks livable with, or you will be joining the endless threads on here about how ridiculous the attacks are

a higher level? I'm in level 28

Your fine at 28.

Just stay out of the exterior of cities and towns at night. If you have to be in a city at night, just be inside a building. If you focus on the DG quest, you stay out of most cities so you can deal with things and have no impact on the towns. Just save before you ever travel to a town or city. If you arrive at night, then you can reload and wait some time so as to arrive in daylight.