Programmatic SEO Search Engine — build it to rank w. AI, stay indexed, % getting Google penalised

We're building a large programmatic SEO site — a search/aggregator style site (think rental aggregator-style listings) that generates high volumes of long-tail landing pages, ranking on Google. The data comes from a crawler feeding a database; you'd own the layer that turns that database into ranking pages. The core challenge we need you to solve: building this with AI at scale while making sure Google doesn't penalize or deindex us for mass-produced AI content. We want someone with hands-on experience who has actually built this and kept it ranking. Be technical and concrete, and explain your reasoning — I'm comparing how different experts think. Please walk us through how you would solve the following: 1. AI without penalties — the crux. What specifically keeps a high-volume AI-generated site from being flagged or deindexed under Helpful Content and spam systems? 2. Where's the line in your experience, and how do you stay on the right side of it? 3. Content at scale — using AI so each page is unique and genuinely useful enough to rank, not thin or duplicate, pulling from a structured database. 4. Architecture — stack, templating, URL structure to scale to 100k+ pages. How the SEO layer connects to the database. 5. Indexing — getting large page volumes indexed, crawl budget, sitemaps, internal linking. How fast is too fast to publish? Do you throttle? 6. E-E-A-T — trust signals for this type of site. Infrastructure & cost — realistic hosting, storage and bandwidth needs, rough monthly cost at 10k / 100k / 1M pages. Static vs dynamic generation? Cheapest sensible setup that still scales, and where not to cut costs? 7. Replication — how you'd structure it so the whole system can be relaunched in a new market/country with minimal rework. 8. Your track record — what you've built, what got penalized, what you'd do differently. Priority is lightweight, low-cost, low-maintenance while handling real volume and with a clear foolproof strategy for not getting flagged or penalised by Google.