After trying many other notation apps I find Newzik to be the top.

For the needs you described it has
- A "Lyrics and chords" mode that allows you to type in or copy paste your L&C.
- It can transpose your L&C file to the desired key
- Library with setlists
- Ability to work offline
- All saved in Newziks cloud so no worries about loosing your data incase something happens to your iPad. You can always access your account from another device.

In add it has
- MusicXML: Ability to import MusicXML files.
- Audio/video/youtube: Ability to import any audio, video or youtube link and attach it to a piece.
- Collaborative Setlists: You can share your markings or any edits in real-time


Hope this helps.
Good luck !