Sushi is fine. The main concern with sushi is obviously the chance of bacterial infection in the context of eating raw fish. Those who make sushi for us to eat undergo rigorous and lengthy training in order to prepare the raw fish in a way that minimizes the chance of infection while allowing us to eat such an awesome delicacy, So, yes, sushi is safe if the correct people are making it.
Perhaps, but rarely. There was a recent outbreak of salmonellosis linked to spicy tuna in sushi rolls that was prepared from 'tuna scrape' produced in the indian subcontinent which had been contaminated during production. Raw fish without human contamination should not cause salmonellosis.
Unlikely. Salmonella is usually contracted from improperly prepared food or an infected source. You can get salmonella from this source but it is unlikely. Most sushi preparation is done properly using good sources of the raw fish. No sushi outfit wants to get a reputation for infecting their customers.