@KoNasl Thanks for reaching out and apologies for delay.
Considering this is yet pre-product and number of objects are less than 100,000 you can go for In-place update for Azure AD connect.
During the update process the synchronization is stopped anyway.
Do remember, If you've made changes to the out-of-box synchronization rules, then these rules are set back to the default configuration on upgrade. To make sure that your configuration is kept between upgrades, make sure that you make changes as they're described in Best practices for changing the default configuration.
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