loading flat file to TEMP table in oracle then move data to real tables

Hi,

desparate situation,can anyone suggest me on this,

my company database is getting data inserted from different exteral source systems,data will come as a flat file,
so,making use of sql loader,UNIX (for batch process) dump data into temp tables then  perform validations and load data into REAL tables,
it looked straight forward when i hear this,but what happend is we dont have any designer to do all the high level design,techinical design,
so,all the process from scrath to end will be done by me,as i am more into coding plsql n never had this sort of exp i need your valuable suggestion to make my job done.
can you please suggest me answers for following questions:

1,design flow diagrams,sequence diagrams to show how flow should follow to each step,

2,all the process should be automated,for this i am thinking off batch process,i have got some basic knowledge of UNIX,

3,writing data abstraction layer to make future changes easy without effecting whole application code(i got no idea how data abstraction layer works),

i am basically oracle PL/SQL guy,i didnt have exp on above requirement but i can do it with your help,i am in desparate situation as i work for financial company,tight timelines,
please help me,your help will be greatly appreciated,
Thanks for having a look into my question n thanks in advance to suggesting me answers