Hi,
As per your description, we have the platform for tenants and landlord which is accessible via web browser. The CRM work flow you have mentioned with add/update/delete, I would also suggest to have a section where a customer can book a ticket for a service request which can be paid or non-paid. So, CRM is related to accounts receivable, buying, selling and also to those which are separately individual modules.
The responsive design will be given as a Bootstrap design with custom framework of PHP since you have given us the freedom to choose. So, we should suggest best quality to you.
I am eager to demonstrate our already made platform in web while our discussion. Looking forward.
Regards,
Mit-