Would a mail-order tune be sufficient for my combination, or is a dyno session required?

A dyno isn't required for most builds, but a pure "bench" tune with no logging is the weakest option.

How remote (mail-order) tuning works — per Casey Rance of MailOrderTuner in LSX Magazine:

• Types: an email or "bench" tune built from your parts list; a street tune, where you datalog while driving and the tuner revises the file; and a dyno tune.
• Process: you fill in a detailed spec form, load the tune with your own HP Tuners interface (with credits on it), log on a safe closed course, send the logs, and get revisions until it's right.
• Pros: no travel or shop backlog, low cost, and it works for engine and transmission swaps.
• Cons: you do the work of collecting good logs, and changing factory settings without expertise carries risk.
• When a dyno is worth it: very high power (he cites 1,000 hp and up) and verifying a new combination, because the dyno shows mechanical problems — such as an engine making less power than it should — that logs alone may not.
• Get the basics right first: he sees fuel pressure that isn't what the owner thinks, MAF sensors in the wrong place or tube size, incomplete setups, and wrong tire and gear data. Verify these before any tune.

Want to do it yourself? See who tunes it, and how to learn.