Build Social Network Audience Profiles using APIs & Data Analysis

We need to build social network audience profiles across multiple networks for a SaaS web app (influencer marketing platform). 1) The user inputs their social profile links for Facebook Pages, Instagram, YouTube and Twitter. It can be any combination of one or more of these. We use oAuth to connect. 2) We retrieve audience insights data like age groups, genders, locations, engagement stats, topics. We save all this to our DB. 3) We build a profile that takes all of the platforms into account and summarises their audience. This is for the benefit of potential advertisers. So for e.g. UserX might have a total reach of 1.5m (500k FB, 500k Twitter, 500k Instagram), the gender split might be 70% female, top age group 18-25, top location USA, topics: fashion, beauty, etc). Brand affinities would also be useful. If you have a look at the sample reports on statsocial.com, this will give you a good idea of what we are looking for (but simpler). We may need to use third party APIs for some of the data based on what we can / can't get directly from the networks. Basically we need to understand an influencers combined audience across platforms, and present this data on a one page profile to potential advertisers. We already use IBM Watson to help us understand topics of blogs, so if your plan includes this please explain. Klout may also be useful. Please use the words 'influencer marketing rocks' in the first sentence or your proposal will be deleted. Please explain your approach, relevant experience, and feel free to ask questions. The app is built on a Yii framework, but we are in the process of switching to a JS Vue front end with API backend. Extra notes: