One model is often enough. But when mistakes matter, a second pass can be worth it.This is a hands-on playbook for orchestrating several AI agents — a builder that drafts, a separately prompted reviewer whose performance you measure, task-specific routing, and source-aware research checks. It is written for solo founders and indie developers who already work with an agent like Claude Code, Codex CLI or Cursor and want a coordinated setup without a machine-learning background or unnecessary complexity. A second model is an option, not a universal requirement.What is inside (ten chapters): Why more than one agent — the principle, a maturity ladder, and an honest account of when one model is enough. The 2026 model landscape — Claude, GPT, Gemini and Grok as flagship / balanced / cheap-fast tiers, with dated, provider-accurate prices and the caching and batch levers that actually move your bill. Open & self-hosted models — Llama, Qwen, DeepSeek, Mistral, gpt-oss: a decision tree for when local is genuinely worth it (hint: usually privacy, not cost). Orchestration patterns — reviewer, planner-executor, router, ensemble, debate, pipeline, orchestrator-worker: what each is for, and what it costs. The reviewer pattern, hands-on — reproduce a builder plus an independent read-only reviewer (Claude Code + Codex-style) step by step, including conflict resolution. Tooling & orchestration stack — Claude Code subagents, Codex CLI, LangGraph, CrewAI, AutoGen, Google ADK, PydanticAI and more, without over-engineering. Deep research in your workflow — how agentic research works, which tools fit, and how to verify it before you build on it. Cost & quality — a cost model, an interactive calculator, and evaluation-led recipes per task type. Safety, security & governance — prompt injection between agents, least privilege, and human-in-the-loop gates. Start now — five copy-paste prompts (planning, setup, review, deep research) and a defensive security-check prompt you run first. Also included: an interactive multi-agent cost calculator, a model-selection matrix (XLSX), an orchestration setup checklist (XLSX), and the full prompt pack as a plain-text file. Everything works offline; the print edition is a 66-page tagged PDF.An honest promise: a separate review pass can reduce missed errors when the exact builder-reviewer pairing performs well on representative evaluations; it can also miss defects or add false positives. This guide gives you a method and a dated snapshot, not a guarantee. Verify current model names, capabilities and prices on the provider's official page before relying on them.Pairs well with: The AI-First Operating Playbook — the business-wide operating system this deep dive plugs into.More details: product page on dargel-solutions.deCreated with AI assistance and quality-assured by a multi-agent review setup; all content was directed, reviewed and refined by the publisher. General information — not legal, tax, financial, or security advice. Sold by Dargel Solutions (Frankfurt am Main) under the pen name Adrian Verdan; small business under § 19 UStG, no VAT shown. Single-user licence.