Convert Joomla 3 to Joomla 4 + add Joomdle extension

I have a highly functioning website (www.transformationalsafety.com) that is in J3.10.11. I am aware support for this version of J shall expire soon. I would like advice on migrating this site to J4. I have always coded my own sites though it may be useful to have a professional view the site. It is built on a purchased template - though removal of that is not a deal-breaker as long as the functionality remains. My plan is to also integrate a new Joomdle installation with the migrated website.