[Dr. Sivana]

Venite igitur, francis!

The expression is idiomatic, so I understand your use of "venite". But literally, doesn't that mean "Therefore, come Francis?".

My limited Latin training makes me want to use "agere" (to drive or do), possibly as a sunjunctive first person plural (ageremur? My memory of the subjunctive is weak)

[Campion]

I think “let’s go Francis” would be imperative, “Ite Francisce!”, or something like it. “Ite Francisce” is “Go, Francis!”. I’m not sure what to do with “Let’s”; it’s idiomatic.