Help me architect this solution

I have a new opportunity, current environment; - 150 users over 4 locations. - 60% windows (single language and pro) - 40% Mac - no AD - lucidlink for file sharing - icewarp for mail - sentinel one for AV - Google docs

They say security is of utmost importance.

We’re primarily a Microsoft house. The client does not want AD or Azure nor any Microsoft subs. The want to use the icewarp and lucidlink. They’re very sticky on to their current solutions.

I feel it plastered, unsecured, scattered and wanting to walk away.

Any suggestions welcome.