Welcome to the community, @AyDee!
In general, if your tables are all communicating with each other, then it is often best to try to build one monolithic base for all of your tables. That’s because you can unleash the full power of Airtable by having everything in one base.
And then, if you’d like to shield certain users from seeing certain tables in your base, you can use interfaces for that. (You can do this by removing your users from their base access first, and adding them only to certain interfaces.)
Syncing is different than linking records. You can link as many records as you want, but linking records is much easier when everything is in one base. Linking records across synced bases opens up an entire host of challenges that need to be accounted for, which is one of the reasons why it’s typically better & easier to keep everything in one base (if you can).
What’s frustrating about Airtable’s support articles is that they are often incorrect. Even though that support article says that you are limited to one sync source per base on the Team plan, I have never seen that limit enforced. I have clients on the Team plan who have 5 different sync sources per base, and it might be possible to have even more than that. The business plan says that they offer up to 50 sync sources per base.
Regarding your email monitoring question:
Airtable’s automations offer the ability to monitor an Outlook inbox for incoming emails, but that’s all that Airtable offers natively.
For anything more advanced than that, you would need to custom-create your own email tracking system.
I’ve heard good things about TaskRobin, but I’ve never used it personally.
For my Airtable consulting clients, I’ve setup advanced email tracking systems that monitor both incoming & outgoing emails — and use other email services besides Outlook — by using Make’s automations & integrations.
If you’ve never used Make before, I’ve assembled a bunch of Make training resources in this thread: Make.com - Basic Training & Navigation Tips
For example, here is how you would instantly trigger a Make automation from Airtable: Instantly trigger a Make.com automation from Airtable (i.e. sending Airtable data to an external webhook such as Make.com)
I also give live demonstrations of how to use Make in many of my BuiltOnAir podcast appearances here.
p.s. If you’d like to hire an expert Airtable consultant to help you with anything Airtable-related, please feel free to contact me through my website: Airtable consultant — ScottWorld