Create connections for different SAS subscriptions like Dapulse, Streak for Gmail, Slack, etc. via each service's RESTful API's

We use many different systems and need to connect them in very specific ways. Each service has a RESTful API. We will be connecting Dapulse, Streak for Gmail, Slack, Pipedrive, Mailchimp, Google Drive, Square, Quickbooks and other programs via their API's. <One example chain> This example includes a "chain" of actions. Streak API: Every time a "box" (client contact) moves from one specific pipeline to another specific pipeline in Streak, initiate action 1. Action 1 via Pipedrive API: Check to see if that box/name/email exists in Pipedrive and, if not, create a new contact. Then initiate action 2. Action 2 via Streak API Later, when that box (client contact) moves to the last pipeline in Streak, now initiate action 3. Action 3 via Dapulse API Create a new pulse in Dapulse and initiate action 4. Action 4 viaDeputy API Check who is currently working in Deputy and send them an email via action 5 Action 5 via Gmail API and Slack API Send a "heads up" email via Gmail and a heads up text via slack to notify the person from action 4 that Action 3 and Action 1 are ready for attention. </One example chain> We have about 5 "chains" consisting of different actions. Each "chain" of actions will be 5-10 actions long. We will give a very detailed description of each action and each chain. Please describe what programming language will be best for this work. We want to have readable, well-documented code.