Why don’t you keep it very simple.
Bonjour sync quickest and simplist. Do what it advises in the DEVONthink Manual. You are using indexed files, so read carefully about that complication.
Supplement that with existing info already here. No need to dig further for other instructions.
Setup the two macs to sync with Bonjour while on your local network. Turn on the MacBook every so often and let it sync with the other Mac. First sync with the volume of data you have may take some time–after that just changes are synced.
Before the trip, sync the MacBook, travel, return and do the sync. Setting up a Bonjour sync is fully described in the DEVONthink Manual. Unless someone back at Global HQ on the other Mac, no need to sync using third party internet service while travelling.