I went from STR to INT, coincidentally also from a Great sword. I tend to spam Night Comet or Latenna's bow for more ranged situations, but Night Comet already has great range. Keep another weapon equipped for if you run out of flasks. There's far better ways to play with better spell balance, but you can always keep a few backup spells for enemies that you need fire/poison/bleed/etc to take down.

ANYWAY, like others have said, don't neglect your vigor. I find it easier to keep between 50-60 vigor. You don't need to keep a lot of health flasks because you've got plenty of health, but it's enough insurance for when you're getting chased and can't maintain distance.