Shopify to Magento Migration / URL Redirects & Search Console Configuration

STATUS: We have a webshop for brushpainting supplies [login to view URL] The shop itself is built on Magento and hosted on Amazon AWS. The blog features like Blog, Gallery, Knowledgebase, Glossary are built on Wordpress. We are in the process of migrating this shop to Shopify. We already moved all the products manually and want to have the URL redirects setup properly (at this point only for the products since the blog has not been moved yet). The products on the current shop have a quite a good organic ranking on Google - 80% of our traffice is either Google Organic (60%) or Pinterest (10%) or Organic Ranking on other search engines. So all our sales come from organic ranking. GOALS: We want to make sure that when migrating to Shopify our shop and the products do not drop in Google ranking. So what we think needs to be done. a/ Inform Google that the an old URL on Magento a1 is now the new URL on Shopify a2 b/ Make sure if a client still has the old links from Mangento there is a redirect to the new Shopify shop QUESTIONS: How long woudl you need for this? What information do you need from us so you can assess approximate time needed for the proper URL redirects and Google Search Consolte setup? When are we save to remove the old shop from Magento? And which steps need to be taken? What needs to be done to avoid Google indexing duplicate content since each product according to the Shopify nomenclature has several URL paths leading to the same product - example: Link 1: [login to view URL] >> via All Products / here also the question why the URL handle is so weird? Link 2: [login to view URL] >> via Collections (Ink Sticks) Link 3: [login to view URL] >> via Collections (Ink / Section Header in Mega Menu)