What comes first?

I'll say CRO to get the most out of your traffic, BUT without traffic you can't test much what's working or not in your website, so after optimizing as much as possible is time to balance both. A bit simplistic the question though, I probably won't start with any of those my business

I don't think they're sequential. SEO should persist through your strategy/approach regardless of which point you're at.

How are you going to drive traffic to your site?

If with SEO, SEO comes first. As soon as you have enough visitors to be able to draw conclusions, you can start on conversion improvement.

TRAFFIC in this scenario, will ALWAYS come first... without consistent traffic flow all of your CRO efforts are absolutely meaningless.

As a CRO provider... traffic is the biggest hurdle to onboarding clients.

If you have say 100 visitors per day its simply not worth your time to even begin with CRO.. not til you get to say 1000 visitors a day does it make sense, and even then you will be testing for in excess of a month to MAYBE get a result worth counting on.

I work on sites that are getting over 30,000 visits per day and we run tests for 15 days to kind of give you an idea of the amount of traffic needed to get decent reliable results from your CRO efforts.

All that being said, you can get the effect of CRO without the testing. when setting up a funnel, an ad, a lander, and a sales page... we will get the ad to a point that it is converting traffic, we then focus on the lander and get it optimized to convert the CTA ( call to action ) and lastly we manipulate the off to get it converting. We call this a base line setup. for many this will be more than enough before you start getting into CRO efforts.

We do these ONE AT A TIME. the minute you start changing this and that across the 3 pages you really dont know whats working and whats not. Each step one at a time is in my opinion best practice.

Hope that Helps!

In most cases, it depends on different factors such as the type of business, the industry you operate in, the level of competition, but, I think the common denominators tend to be similar.

Branding. How can your audience look you up without knowing your brand?

I would say SEO, it's the most advantageous option
you're profit actually depends on both of this factors

Hi
There is no first or second. You have to take both of these simultaneously. The very first, optimize your website for users as well as for search engines. Once it's done start doing off-page activities, build quality backlinks from niche websites to rank web pages and drive traffic to the website.
If you go with the CRO first then how would you track conversions when you have no visits or users on your website?