Hi Anil,
I can only answer 1. and 2. (and would be interested into 3. as well):
1.
Yes you can access tables from a different schema and also HANA views. In this case no 'using' is needed.
Examples:
RESULT = SELECT
…
FROM
"SAP_ECC"."T441V" AS t,
"_SYS_BIC"."tmp.package/AFPO" AS a.
WHERE ...
2. In this case, if you need schema mapping: You could use HANA (projection) views which just forward to a different schema, also see example.
Best regards,
Christoph