Businesses of all sizes looking to provide their customers with a direct channel of communication and support are eligible to apply. However, certain business can't apply, for more information refer this link.
WhatsApp for business is still in an early access phase, and open to limited number of businesses today. The approval for this access is determined by WhatsApp, after looking into specific use cases, messaging volumes per day (only businesses with significant volumes or clear growth plans in under 90 days will be onboarded), overall reach, internal KPIs to determine success of Whatsapp as a channel. WhatsApp will review each submission on a case-by-case basis. If you have an existing relationship with Facebook do mention the same at the time of application.
Freshchat does not directly support proactive/template messages yet. Also, please note that there are separate costs associated with the WhatsApp Business integration and it is available starting from Garden plan of Freshchat.