The best place to stay close to the 7 Sacred pools is Travasa near Hana (the only hotel in Hana), on the East side of the island, which is in the middle of nowhere. Good snorkeling is really on the south or west sides of the island about 2.5 hours drive away. Yes, Hana it is only about 45 miles away from Kahului (the major central city), but the road has 45 one lane bridges on it where you have to wait for traffic. Average speed tops out at 25 miles per hour.
The best place to stay is in the Wailea area, also known as Kihei; that is one of the largest resort areas of the island. Kahului only has two very small hotels which are not great. Yes, Kahului is the central hub for business, but you don't want to stay there, it isn't pretty. Kihei has tons of condos to rent and Beautiful resorts.
7 sacred pools is about a 2.75 hour drive from Kihei or Wailea.
You are wanting to do activities that are unfortunately on completely different sides of the island.
Also, the bus system is inadequate on Maui. Not set up for travelers, basically for the working public. No bus goes to Hana unless it is a tour bus, which may be a good option for you.