The main authority on the capsule wardrobe movement is Caroline Rector who is also the creator of Unfancy.com, where you can find tons of resources on creating capsule collections
Caroline recommends 37 items as the golden number and varies by season. You should take what you have in your closet now, size it down to 37 wearable items, and then test wear only those items for 3 months.
No 2 people will have the same wardrobe needs so 37 may not work for you. I like to keep mine between 25 to 50 pieces but yours can easily go below 25 or above 50.