Create connections between Dapulse, Streak for Gmail, Slack, etc. via RESTful API's

Our company uses many disconnected systems. We 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. <Example> 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. </Example> All of these actions will be very simple and 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.