Some of the castes in Sri Lanka are  Bathgama, Badal, Durava, Govigama, Karava, Navandanna, Rajaka, Salagama, Vahumpura, ,

Yes most of them do have traditional occupations such as smithery, pottery, candy making, dairy farming, laundering, drumming, etc. However apart from their specialized occupations, all castes also engaged in cultivating paddy on the lands tenanted by them.

Yes they do. The Salagama caste was in the forefront to break the Siyam Nikaya   Govigama monopoly on the Buddhist Sangha. They set up the Amarapura Mulawansa Nikaya. The Durava caste has produced leading entrepreneurs such as N. U. Jayawardena and the Raja Nanayakkara family. Other less well known castes too have produced their share of businessmen , professionals and good citizens. However as long as the Govigama monopoly on politics and Buddhism remain, none of them can become a President, Prime minister or national leader. Salagama C. P. de Silva was sent off as an ambassador to enable Dudley Senanayake to become the Prime Minister. There are many such examples.

Yes many of the minority castes have already disappeared. A study of family name change notices published in newspapers indicate that most castes are merging with the Govigama caste. Inter-caste marriages are not uncommon now but you can still see the castes of both parents mentioned in marriage proposal advertisements, probably because it is still relevant for society.