Will there be sentences like "hello my name is..."?
Unlikely. Duolingo tries to teach the basics of sentence construction so you can create your own sentences. There are usually plenty of phrasebook type sites. Although the bots do let you hold simple conversations for those languages which have the bots.
I do not know, but if you just want to know how to say that simply:
Hajimemashite. Watashi wa [name] desu.
Or more casually: Hajimemashite. [Name] desu.
If you want to be more polite/formal you can do:
Hajimemashite. [Name] to moushimasu. (I am (humbly) called [name].)
(A literal way to say "my name is" would be: Watashi no namae wa [name] desu. But you probably don't need to say this entire sentence in an introductory conversation.)
I think some other language trees I've used have included conversational phrase lessons. Maybe as the Japanese course gets more developed they will add that? (Edit: Looks like there is a greetings section, I just tested out of it, whoops. Maybe they'll add more phrases to it?)