A few more things to consider

We looked at the different acquisition channels at a high level. There is a lot more detail you could look into for some of these channels.

Adwords Report
We already pointed out that you can link your adwords account to Google Analytics so you can study more detail behind the traffic coming in from your pay per click campaigns and include costs in that assessment.

I have included the link with more info on how this works again below.
https://support.google.com/adwords/answer/1704341?hl=en

Search Console Report

The Search Console report gives you more information related to your organic search traffic. For any given landing page on your site, this report tells you how often a link to this landing page was viewed in search results and it gives you an idea of the associated keywords and the clicks on them.
In order to see these data, you need to enable the integration of your search data in your analytics reports. You can take this step in the property settings.

Helpful Links:

Social Report

The Social report allows you to dig a bit deeper into the social referral traffic. What networks do people come from, and which URLs were shared? That is the type of information you can find out here. It can be a first helpful step in understanding which of your social marketing efforts pay off most. For instance, if you are very active on Twitter, but very little traffic comes to your site via the posts you share on Twitter, you may want to assess whether this is worth your time. On the other hand, you may get surprised about certain social networks working better for you than you expected.

More information on social reports:

https://support.google.com/analytics/answer/1683971?hl=en&ref_topic=1316551

Campaigns

The campaigns report puts all of your paid marketing efforts in one place, at least, as long as you have tagged them all with UTM codes. This report can come in handy when you are running a campaign for which you are using different channels. In that case, you can find all the traffic for that campaign bundled together in these reports. Say, for instance that Beta Brand is launching a new Down jacket that was just released. They may do this with display ads, some search ads and an e-mail campaign. This report will allow Beta brand to see all the incoming traffic together under the name of the campaign.

More info on campaign reports:
https://support.google.com/analytics/answer/1033863?hl=en&ref_topic=1032998