2.Can the upgrade and unicode conversion be performed as a continuous process? If yes, what could be the expected downtime?
All this does not apply to your environment. Non-Unicode, single code pages systems are still supported in ECC 6.0. You have to option to an upgrade to ECC 6.0 and migrate to Unicode at a later stage. If you want, you can also do a combined Unicode conversion / release upgrade project which does both in one step.
I cannot predict the expected downtime as it depends on many different factors such as the database size, size of the biggest table, number of CPUs and amount of memory in your system.
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