Hi,
First time in Aruba? I will be in Aruba ~one-month after you but I visit annually. I stay in Oranjestad in the Marriott Renaissance Ocean Suites (two weeks of time share).
I will provide first some diving / snorkel info and then some general dining suggestions.
I dive with S.E.Aruba Fly ’n Dive http://www.se-aruba.com/ which is located between Oranjestad and the airport. I can’t recommend them highly enough. Both my daughter and I have taken our open water and advanced courses with them and as far as recreational diving, they provide access to all the Aruba sites and I have seen non-divers also ride along in many occasions. Regardless of where you stay they will pick you up and so their location is not a problem plus they are close by boat to a majority of the dive sites.
For snorkeling there are the usual tours. There is a decent catamaran three-stop morning or afternoon sail with alcohol and food. You get a wreck and two reefs. The two reefs are also accessible by land if you so desire but you may need to get there by bus or car but access is free. Snorkeling off the beaches at the high-rise hotels would not impress much; sandy and shallow. Below the airport is Baby Beach which is great, but again you may need a car or tour to get there. A second sail which we like is with Anthony on the Tranquilo http://www.tranquiloaruba.com/ . This is a day sail 2-hrs out along the island to a great snorkeling spot, lunch and a 2-hr sail back. There is a very shallow snorkel spot that is surrounded by coral and so you are "in the fish bowl" so-to-speak and is very nice. Anthony also takes you out , if you want, on a drift snorkel and this is not to be missied if you like deep-colors, huge barrel formations and the usual suspects for fish and other coral, depending on your tolerance this may be pricey but it is a great day! Again this is Aruba and so beverages are also free-flowing :)
For dining http://www.restaurantsaruba.com/all.html our favorites are Madam Janette, Pinchos, LG Smith, Que Pasa, Caffe Baci, Gianni’s, Rumba, Scandals, Yemanja ... I am sure that I missed some :)