If you take 3 pills, then take 300mg of powder. 'Molly' isn't necessarily stronger than 'pills' they're the same drug, you'll need the same amount of it no matter what. Though pills vary in the amount of MDMA in them (from 60-120mg usually) so does 'molly' so 100mg is usually as safe bet to be somewhat equal to one pill.
Oh, and just parachute it. There's not really any need for you to buy gel caps. If that's what they come in, fine, but if it comes in powder form, just wrap it in toilet paper and swallow it.