1) I believe you are essentially correct. If is only in version updates that modify the table blocks, like Oracle 7 - Oracle 8 where the ROWID format changed, that the size of the database matters. It's possible if one database had more objects, it would have more metadata in the data dictionary and that would affect the upgrade time, but for the most part, upgrade time is not affected by database size.
3) The database will start and it will not be a proper 11.2 database as it has not been upgraded, but I would not count on it functioning properly. The Oracle binaries would be trying to function with an Oracle 11.2 database, but the database would be 10.2. The manual upgrade is outlined here:http://www.oracle-base.com/articles/11g ... rade_paths