A ORM layer is appealing.
However, in practice I either write simple ORM myself or use the Content Provider paradigm, which does not cooperate well with ORM.
I have looked into some existing ORM libraries (mainly ORMLite ,activeAnroid) but they all scared me away
as they seems not so easy to get started.
"We're talking about 25-30 unique tables, and at least 10 table joins.
About 300-500 unique fields (columns)"
If you have fixed and limited patterns of how the data will be queried, I would recommend to write the ORM/sql yourself.
My 2 cents.