1) Do you plan to

a) parse the XML docs and store them into multiple relational tables   ?

If so, what languages or techniques do you intend to use to accomplish this?

b) store an XML doc in a single XMLType column in the Oracle database?

Do you need to index the data to perform XML or "free text" searches?

If so, what XPATH indexing do you intend to perform?

c) Register XSD as an XML Schema and have Oracle validate incoming XML documents such that
data is automatically shredded into object-relational tables based upon the different
types and attributes?

If you choose (c), how will you reload and revalidate data against the new XSD should
new data elements become available in the XSD?

2) How important is it to preserve the exact XML document ingested in Oracle?

About Character Large Objects (CLOBs)

Yes, you can store CLOBs in line with a database row up to 4,000 characters, else it's written to a separate LOB segment.

Oracle automatically creates LOB indexes whether you want them or not, so you might want to review the non-XML CLOBS in your design and determine whether they would be well under the 4,000 characters and thus fit into a VARCHAR2 data column.