In Season 1, Koushiro theorized that they didn't need to eat or go the bathroom, but the Chosen never tested that theory. Seeing as the Zero-two gain spent time getting food during their adventures, it's safe to say that Tai and the others would still go for food in the Digital World as well.
For the most part, anyone except Ryo and maybe Alice, would find obtaining food for themselves as being important out of habit. Most of them wouldn't know that they didn't need to eat and do it becuase they believe they have to. If they spent long enough time in the Digital World, they would eventually learn they didn't need to, but that could take years or very shitty living conditions where food isn't available.
Simple point, any human in the Digital World will not starve to death.
Daniel, I don't think you're paying attention. In some ways, I've already answered all these questions.
How about if I wrote a season 2 and season 3 cross-over lemon? When the season 2 people entered season 3 world, they don't need foods too, right?
Tai and the others DO NOT NEED FOOD IN THEIR OWN DIGITAL WORLD, THEY ONLY _THINK_ THEY DO. They NEVER tested Koushiro's theory, but the basic laws of physics that kept Ryo from needing food applies to their Digital World as well.
Being in the Tamers Digital World CHANGES NOTHING in that regard.
Was Gennai still alive in season 3? If Digimon does not aged, Gennai should still alive somewhere in season 3.
Wrong dimension. He doesn't exist in Season 3 as he was never born to that world.
In season 3, for those Digimon who wore clothes, for e.g. Leomon, if his pants was torn (may be during a battle), does he need money to buy a new one? Or how did he repair the torn pants? And for those who has weapons, for e.g. Leomon's dagger. If his dagger was borken, where could he buy a new one? If their armors were damaged, who would repair for them? And how?
Doesn't matter which season, including season 4, a digimon's clothes, weapons, armor, whatever are part of the digimon. If Leomon's pants rip, they will heal themselves much as if he got a cut. If his sword breaks, it will regenerate. If they are lost, a new one will form. And with a Digimon speed of recovery, they would only be out the item for a few days at most. (Leomon without pants for a few days would be funny.)