Multi-Client CRM setup. Thinking Go High Level, or other if you can propose better

I run a busy marketing agency and need a single CRM that keeps each client’s data separate yet lets my team move effortlessly between accounts. The build must connect to our preferred VOIP dialing tool (dialpad) and the main social media platforms so campaign metrics, conversations and scheduled posts flow straight into the right contact records.

Day-to-day, my staff should be able to handle contact management, place calls through Dialpad in-browser, and drop Calendly links that automatically log meetings. Beyond those basics I want room to grow, so custom workflows and automations are essential—for instance, we run adverts from clients' meta accounts and I want any lead form filled in to go into their database and would trigger an SMS sequence and assign a follow-up call without human intervention.

I’m open to whatever stack you recommend—HubSpot, Zoho, GoHighLevel, or a carefully selected open-source suite—provided the end result is stable, scalable, and delivers the integrations listed above. When you respond, outline:
• the platform you’d use and why
• how you’ll map data between tools
• estimated timeline for turning over a fully tested system

Deliverables will be accepted once I can run a live campaign through one client workspace and see emails, social interactions, calls, and meetings captured end-to-end. Ongoing optimisation work is on the table after that first milestone is met.

See the file for some questions that were asked by someone and gives more insight