LLM Content-Generation SaaS with Templates, Editor and Usage Limits

We are launching a niche AI writing product and need an experienced team to build a content-generation web application from the ground up. The core idea is simple: a user enters a topic or a short brief, picks a template, and receives ready-to-use marketing copy generated on top of a large language model API. We want a fast, reliable editor where the result can be refined, regenerated and exported, plus a library of templates for landing pages, product descriptions, email campaigns, social posts and ad headlines. The tone and length of each output should be controllable, and drafts must be easy to save and reopen later.

The service must support user accounts with registration, authentication, saved history of every generation, and folders for organizing drafts. We plan a subscription model, so usage limits and quotas per plan are essential: token or word counters, monthly caps, and graceful handling when a limit is reached. Billing hooks, plan upgrades and a transparent usage dashboard should be part of the first release. Prompt engineering lives on the backend, so each template maps to a tuned instruction and the model provider can be swapped without touching the interface.

Technically we expect a modern stack, a clean REST or streaming interface between the frontend and our server, queueing for long requests, and caching to keep model costs under control. We care about response latency, moderation of generated text, and protection against prompt injection and abuse. Please propose an architecture, a rough timeline and an estimate, describe similar products you have shipped, and explain how you would keep the monthly bill for the language model predictable.

— Template library with adjustable tone, length and language
— Accounts, saved history, folders and export
— Per-plan quotas, counters and billing hooks
— Streaming responses, caching and abuse protection