WordPress theme migration — move from a legacy custom theme to a modern block theme

Overview We run an established (15+ year), appointment-only studio with a staff directory. The site is self-hosted WordPress, currently on an obsolete (~2018) custom theme. We want it migrated to a modern, fast, mobile-first block theme- Kadence or Blocksy (open to your recommendation between the two). This is a migration and restyle of an existing site- not a redesign of our brand, and not a build from scratch. Our content, copy, and structure already exist and should be carried across. We are not looking for new branding, new copy, or a theme's demo content. Why we're doing this The current theme renders navigation and buttons as image files, uses legacy spacer graphics for layout, isn't responsive, loads slowly, and bakes page content and SEO metadata into the theme files so they can't be edited from the WordPress admin. We want the same brand feel and content on a modern foundation that's fast, mobile-friendly, ranks properly, and is editable by our staff. Scope of work Set up a Kadence or Blocksy block theme (not a page builder such as Elementor or Divi). Rebuild our existing pages in the block editor, porting our existing copy across verbatim. Replace image-based navigation and buttons with real text/links; remove legacy spacer graphics; deliver a genuinely responsive, mobile-first, fast layout. Migrate and preserve our existing ACF custom post type for team-member profiles- structured fields (short bio plus several detail fields) and multiple photo galleries per profile. Preserve the ability to manually set the order team members appear in (drag-and-drop ordering is fine). Preserve our separate archive of former team members- their profiles and galleries- driven by an existing current-vs-past status (moving someone to the archive should stay a simple status change). Install and configure an SEO plugin (Rank Math or Yoast); replace outdated site-wide metadata (title / description / Open Graph) that is currently hardcoded in the old theme- we'll supply the corrected values. Confirm the old hardcoded values no longer output anywhere. Clean up image alt text per a checklist we'll provide. Fix our contact form's email deliverability: route outgoing mail through authenticated SMTP (e.g., WP Mail SMTP or FluentSMTP) via a provider we specify, add an instant auto-acknowledgment to the person inquiring, and surface our phone number in the form flow. Switch internal http:// links to https://; remove embedded geo-coordinate metadata from page headers. Must be preserved (this is the core of the job) All existing copy, verbatim, unless we approve a change. The ACF custom-post-type structure, per-profile galleries, and manual ordering. All existing URLs/permalinks and our 15-year domain authority- set up 301 redirects only where a slug genuinely must change. All existing content and photography. Design direction Keep the brand's dark, premium, editorial mood and our existing professional photography. Modernize the execution only- real typography instead of image text, clean contemporary spacing instead of decorative frames, responsive galleries. Do not redesign the brand identity or rewrite copy. Treat the block theme as a clean foundation to style toward our brand — not as a demo to adopt. Mood reference sites (for visual direction, not content): [attach 2–3 dark/premium/editorial sites you like]. Out of scope- please do not touch A community/members area runs on separate forum software (Invision Community) with its own user base. Do not modify it; preserve all of its URLs and links to it intact. Server, DNS, and PHP are managed by our separate system administrator. Coordinate with them on anything that needs a DNS record (e.g., SMTP provider SPF/DKIM) or a PHP version bump, but do not change server-level configuration. Environment Self-hosted WordPress on a VPS, behind Cloudflare; ACF in use; email on a privacy-focused host; current theme is a custom legacy theme. What we'll provide A dedicated admin account and a staging environment. Final approved copy, the exact replacement values for metadata and alt text, and the mood reference sites. A single point of contact. (We keep our specific business details private until we engage- we're glad to share the staging URL and full context directly once we've confirmed fit.) Engagement We'd prefer a fixed-price estimate against this scope, structured as: staging build → our review → live cutover, with a backup and rollback plan. Please confirm in your proposal: You've migrated ACF custom-post-type + gallery content onto a new theme before (briefly, how you approach it). Your approach to preserving URLs and SEO during a theme migration. Your staging, backup, and rollback process for changing the theme on a live site.