Some help needed: changing bar line, deviding piano

Hi,
I attache a couple of lines, a "piano overture" which I created originally using the sequencer and
then exported the MIDI-file (MusicXML not supported in the seq.).

I´ve tried to do the following edits by reading the MuseScore manual but havent managed to do these,
I wonder if someone can help me:

1. How devide the piano part to right and left hand in reasonable way: I know the righ mouse click command "devide" where the defaul devision line is in C3 but with that nor by other devision points I don´t manage to get
the left hand as I´ve played it: e.g. in the first bar(s) left hand play just single notes
H-G, C#-A, D#-H, and the last 6 bars the left hand plays single note-pairs. C#-G, C#-G, C#-G, C#-G, C#-G, C#-G.
2. The first bar should reach until the mark "A", can´t manage to change the bar lines, the time signature
can be changed of course, too.).

Harry

Edit: Attachment removed by request of the poster.