I just launched an online store. What 3rd party tools should be the first to employ? I.e product reviews, email marketing, social

Hate to say it, but it depends. I run a store that isn't particularly social in nature - so social media may not even be integrated. But, recommendations and validation are really important in the market - so featuring and encouraging reviews is key. It really starts with understanding your consumer. What checkpoints do they have to go through before making a purchase? What kind of doubts do they need to overcome? What are the main points of comparison for products in my market? The answers to those questions will drive your decision more than anything else, IMO.

First, congratulations on a new launch. As a rule, in the early stages of a lunch one of your biggest challenges is to build trust.    Trust in that you are real site, that your goods are solid and that you will deliver on whatever you are selling.   A trust worthy site will further help you with your conversion rate, engagement, etc. So,  if you agree with me that trust is the key ingredient to bake in at the early start of a site, lets look at some if the trust ingredients you can fold into your site. First,  solid SSL cert - Verisign is. Good third party investment.   Little work on your part, but the branding value and trust value is high. Money back guarantee, although not purely 3rd party, needs to be mentioned in the same breath as trust.   Review module is good of course, but it can take many years to seed it with enough reviews to make it useful - hence I would instead in the early stage opt out for a "customer comments" section where you start to dump in any positive comments you get from your customers.  And as tempting as it may be, don't put in any fake, self generated comments.  First,  it's just not cool and second, unless its real it won't have the same effect.  People can tell real vs fake - so keep it real. Another module that is good at early stage is a newsletter function.  I won't go into the details here but a "give free info" for email address is a good start.   The signups add up and 6 months later when you are ready to go into 2nd of site growth it will be useful. If you notice,  FB is not on this list as that is a nice step for stage 3+ of site dev. So, in summary, in early stage, your goal is to build trust - build it fast with little effort and not a lot of expense. As another poster indicated,  Analytics is a must, however Analytics will not give you usefully data for a few months - so you certainly want to start gathering it ASAP, but be sure to make site changes decisions from it only on a macro (few months of data) level - otherwise you may end up chasing your own tale,. Once your site growns up a touch, and you are ready to start making site changes, Analytics a/b testing will become your next tool of choice. Best of luck

You are starting a new store, so you need to drive traffic to your site, then analyze where the traffic came from so you know where to spend your marketing time and dollars.

If you are starting a new store without a house list, then I don't think email is first priority. analytics (Google is free) email signup social links reviews