Advice on migrating existing site from Shopify to Wordpress

We've got the front end of our website on Shopify but we don't use any of the eCommerce elements as we have a custom-built back-end and checkout. As such, we have limited value in staying on the Shopify front end and are planning a migration to Wordpress. 

We're taking the opportunity to re-design the website and bring it up to better branding / content / CX standards. 

Where are we now?
* At the moment about 85 - 90% of our traffic comes from paid sources. That said, we do receive a decent trickle of direct traffic to some of our blogs
* Our paid traffic lands on a separate URL (on Wordpress) as we couldn't achieve the UX we needed on Shopify

* Website URL: https://chequp.com/ (shopify)
* Current paid-traffic landing page https://go.chequp.com/mon/ (Wordpress)

We're looking for some guidance on how to safely move from shopify to wordpress including:

* Are there any automations that will help move content across platforms or not?
* Is there any content that's highly valuable for SEO that we should prioritise keeping? 
* What impact should we expect on traffic when we switch over?
* Should we have separate landing pages to receive paid traffic that are detached from the main site? (our ad agency are recommending this approach but we're not so sure!)
* How do we safely move our blogs and keep the SEO value?

Scope:
* Guidance on the migration including an assessment of the SEO-rich content that we need to keep
* What can we do to speed up the migration?
*Risks / issues / watch-outs in terms of business performance

Please could you let me know if this is something you can help us with and an approximate cost to support? Happy to discuss further to help your response.

Thanks,
Vicky