75 ml would be a smallish feed, but it might be okay for a dream feed at this age. Amounts are tricky, especially if you're only looking to do that feed with a bottle. When are you pumping for the feed? Have you just started pumping?
Definitely do not give your baby water at this age, breastfed babies shouldn't get water for several more months.
I always did the dream feed straight from the breast - I would let my LOs nurse until they moved away from that steady suck-swallow pattern and into more of a comfort nursing pattern and then I would unlatch and do the other side. Once they finished the other side, I would rub their backs a touch and put them back in bed. It definitely didn't take longer than 20 minutes, probably closer to 10 once we got going.