Old Goa is the former colonial capital of Goa. Full of history, it today is home to some scenic churches and convents, that are well maintained and worth a visit. Make sure you have at least half-a-day to adequately understand and appreciate the place. The site is maintained by the Archaelogocal Survey of India, and is a UNESCO listed World Heritage site.
Panjim (Panaji), the state-capital of Goa, is barley 9 kms from here. So it is easy to take a bus from Panjim to Old Goa. Private vehicles too ply, but taxis tend to overcharge in Goa.
It is best to visit the place on foot, since there is so much of history to seep in. Local guides, some approved by the tourism department of Goa, are available.
Spend time walking around the monuments and see how Old Goa fits into global history and the meeting points of cultures of another century.
Souvenir and trinklet stalls here, but Panjim has a better choice nearby. Visit the shop at the Museum of Christian Art, at the annexe to the Santa Monica Convent. Worthy of a visit, and reasonably priced.
Options for food and drink are limited in Old Goa. There are a few restaurants in the area, and along the highway that passes through the area.
See above comment.
This isn't a good place at which to cast anchor. Accommodation options are limited. It's best to stay at Panjim or elsewhere in Goa, as travel within the small region tends to be easy -- even if traffic jams are a growing reality due, in part, to the spurt in tourism.
Nearest hotels are in Panjim, though there are a few in the locality too.
Usually by bus. The Konkan Railway has a nearby station, known by the village name of Karmali.