Partitioning A Table In Production?

Oracle 10.2.0.4

I partitioned a source table of around 100 million rows (62GB) in DEV server. The target database was created new. It was range partioned on a date column as follows:

PARTITION BY RANGE (ENTRY_DATE_TIME)
(
PARTITION ppre2012 values less than (TO_DATE('01/01/2012','DD/MM/YYYY')) TABLESPACE WST_LRG_D,
PARTITION p2012 values less than (TO_DATE('01/01/2013','DD/MM/YYYY')) TABLESPACE WST_LRG_D,
PARTITION p2013 values less than (TO_DATE('01/01/2014','DD/MM/YYYY')) TABLESPACE WST_LRG_D,
PARTITION p2014 values less than (MAXVALUE) TABLESPACE WST_LRG_D
)

That is yearly basis. Anything before 2012 went to ppre2012, then p2012, p2013 and so forth. There is 20 million rows in p2012. and around 75 million rows in ppre2012. We needed both the source (un-partitioned) and target (partitioned) tables in DEv for comparision. The queries are normally on the current year partition. Just to state taht I am a developer and don't have full visibility to the production instance.

Now that our tests are complete, we would like to promote this in production. Obviously in production we would not not need both source and target tables. In all probability this will be performed over a weekend window. Therefore I would like to suggest the following .

1) use expdp to export source table
2) drop the source table
3) create a new source table "partitioned" with no indexes
4) use impdp to get data back into table
5) create global index (it is a unique index to enforce uniquness) and the rest of indexes as local
6) perform dbms_stats.gather_table_stats(user,'SOURCE', cascade=>true). This takes around 2 hours in dev

My point is that whether importing 100 million rows will not cause issues with undo segments. Can we import data say first to the current partition p2012 (20 million rows) first.