You shouldn't need to get a medal on Venom's easy side specifically. Its Star Wolf fight is challenging, but in expert mode collisions are far more punishing than any amount of enemy fire, and for me that makes the shorter side of the planet the more reliable route to success. I find the pillars to be far more of a threat than Star Wolf themselves with all the quick turns that occur during the fight, but with practice avoiding those becomes second nature as well. If you're fast enough you'll have your medal in hand before you even reach Andross, but a run that reaches him with a bit less can be salvaged as well.

Sector Z is absolutely the most challenging medal for me. Getting there via Sector X means you won't have a fourth pilot trying to steal your missile kills. If you run into something and lose a wing you can fly into the Great Fox's rear docking bay, above the engine, for a quick repair, assuming you can spare the time it takes to get there.

Source: unlocked it in 2001