Hello all :)

I have Exchange 2007 SP3 servers, Exchange 2013 CU3 (all rules, no dag) in hybrid with Office 365.All mailboxes which intended for migration were migrated. Some of the mailboxes which can't be migrated , for them I would like to install Exchange 2013 CU7 DAG. Current exchange 2013 CU3 servers don't store mailboxes and don't take part in mail flow ( were used for migration to Office 365 only).

My steps:

1) Upgrading Schema, Installing 2 exchange 2013 CU7 servers with mailbox rule  on windows 2008 r2 enterprise (for DAG)

2) Upgrading Exchange CU3 hybrid servers to CU7 ( all rules), but configuring them only as Client servers. Installing NLB mail flow from perimeter Linux postfix servers

3) Upgrading rest CU3 servers to CU7 ( by the time will be removed anyway) - Microsoft does not suggest to keep different versions for weeks/months

4) Testing DAG, Mail flow etc. and migration from exchange 2007.

My questions:

1)Is it ok first to install exchange from scratch on new servers and only then upgrade already working servers?

2) Current 2 Hybrid Servers have all rules installed. I don't really need mailbox rule on them, but I am afraid that if I remove exchange (CU3) and reinstall CU7 with only client rule- I will break hybrid configuration ( so will need to re-run it) and it's not a great fun...( in enterprise :)) . Someone tried that? What to do? To leave as I wrote with all rules? Or reinstall exchange with only Client rule? OS is Exchange 2008 R2 Standard, so DAG will not work anyway.

Also , will it break hybrid config?

3) Can I leave rest exchange 2013 CU3 without upgrading? I will demote them anyway with exchange 2007 after migration.

4) We have exchange 2007 public folders which published to Office 365 using proxy mailbox (with remote config using "set-organisati....). Will it be influenced somehow by actions listed above?

Thanks for all in advance :)