Modifications to WordPress/WooCommerce website

We have a draft WordPress/WooCommerce-enabled website which we wish to go live later next week. There are some changes to the appearance and layout required, and the site will need to transfer to the correct domain in order to be live. The theme is a Divi child theme and we wish all changes to not be lost when updates are applied in future, therefore no custom coding is preferable. The site already has a number of plugins for appearance and layout anyway. We would like the option to have a full width page and slide layout, without custom code, but need to see it first in case it doesn't work well. Currently, the site loads slowly and we would like this fixed. It could be because it is a draft site restored from a different domain, but it is very slow to load. We'd like the Divido logo (a credit option next to applicable products) to be perhaps 2x bigger. We need help with the postage configuration. We'd like it to be free only for UK orders over £100, otherwise based on weight using UK UPS or Royal Mail/ParcelForce rates, but we'll need to add the weights shortly. If a plugin is available we're happy to pay and use that. The Testimonials feature needs tidying up. We want website users to be able to post a testimonial/review and for it to be accessible from the Testimonials top link - it's installed but not linked or properly configured. All changes must be properly documented, so we know what's been done.