Should I build one agent or a team of agents working together?

Start with one. The famous industry debate (Cognition's "Don't Build Multi-Agents" vs Anthropic's multi-agent research system) actually agrees on the fundamentals: multiple agents working from partial context make conflicting decisions, and multi-agent setups burn roughly 15x the tokens. Go multi-agent only when the work is genuinely parallelizable and read-heavy, like broad research, and even then use one lead agent delegating to sub-agents, not a committee of equals.