Need Suggestion

I am conversant with Oracle v 9i (back-end) and also its native front-end component - Developer suite 6i/9i/10g.I do not have in depth knowledge of architecture or DBA part of Oracle although, I have some idea.
Please clarify the following:
a) Which is the version of Oracle currently running in the market w r t back-end - Oracle 9i / 10g.
b) Prospects of Oracle's native front-end - Developer suite 6i/9i/10g in the market and also w r t career.
c) What is Oracle Apps or 11i?
d) Which certification - DBA track, Developer track, Oracle apps / 11i,Datawarehouse
e) Datawarehouse / Data mining as a career?
f) Tools /subjects w r t Datawarehouse / Data mining - like Informatica, etc
g) ERP, SAP w r t Oracle
h) Any other tools / subjects to know w r t Oracle?
i) How about UNIX / Linux along with Oracle?

Could any of you suggest the best possible path or solution. I would be grateful to you all.
Thanks and Regards,