Hi Sri Sri
For (1) and (2) is possible to by maintaining values for account keys ESA and ESE in your tax code using FTXP.
For the above example maintain 12.3% in ESA and -12.3% in ESE
Then maintain posting account for them in OB40
ESA - Service tax 2 a/c
ESE - Cenvat on Service tax 1 a/c
I do not know about (3) partial payment scenario,
Regards
Sach!n