Learn Portuguese (Portugal): O comediante estava a gesticular muito no palco. - The comedian was gesticulating a lot on the stage.

You would use por muito que (however much) followed by the subjunctive. Because the main sentence is in the past (estava), you need the imperfect subjunctive: Por muito que o comediante estivesse a gesticular no palco...

Could I use cena instead of palco for 'stage' here?

Not exactly. Palco refers specifically to the physical raised platform the comedian is standing on. Cena usually means a 'scene' in a play or film, or is used in fixed expressions like entrar em cena (to go on stage or enter the scene).

As a refresher, why is it estava a gesticular and not estava gesticulando?

In European Portuguese, continuous actions are almost always formed with estar a plus the infinitive of the verb. While estava gesticulando (using the gerund) is grammatically correct and standard in Brazil, it sounds unnatural in Portugal for this everyday context.

The word comediante ends in '-e'. Does it change if the comedian is a woman?

No, comediante is an invariable noun for both genders. The word itself stays the same, so you only change the article to indicate gender: a comediante for a female comedian, and o comediante for a male one.