Goku could escape by overpowering Broly. He might tap into his Super Saiyan forms, like going into Super Saiyan Blue or even Ultra Instinct if he's pushed far enough. His sheer power and fighting skills could allow him to break free from whatever restraints Broly has put on him.
A Goku and Goku Black fusion in fanfiction could be really exciting. The fusion would inherit Goku's love for fighting and getting stronger, but also Goku Black's ambition. Their combined ki could be a new type of energy that no one has ever seen before. This new fused form might also have new transformations or abilities. For example, it could combine Goku's Super Saiyan forms with Goku Black's Rose form in unexpected ways. It could change the power balance in the Dragon Ball world and open up all sorts of new storylines, like teaming up with other characters to take on new threats or even having internal struggles between the two personalities within the fusion.
It could be insanely powerful. Goku already has incredible power levels, and Goku Black is no slouch either. When they fuse, it's like combining two nuclear reactors. Their power could be so great that they could effortlessly destroy planets just by flexing their newfound power. They might be able to reach Super Saiyan forms that are far beyond what we've seen in the official series, with power levels that are basically off the scale.
Sure. Fanfiction writers have a lot of creative freedom when it comes to Goku and Female Broly. In some fanfictions, they might be in a romantic relationship, which is an interesting take considering their Saiyan heritage and the way they both value strength. However, not all fanfictions take this route. Some might explore a more platonic friendship where they respect each other's power and learn from one another. You can usually find a variety of these stories by using the search function on major fanfiction platforms.
I think Zeno would be a really tough opponent. Zeno has the power to erase entire universes, and a Goku and Goku Black fusion, despite being extremely powerful, would have a hard time against such a being with god - like powers.
One common theme is redemption. Since Broly is often portrayed as a villain initially, many fanfics focus on his journey towards redemption with Goku's help. For example, Goku might show Broly a different way of using his power, leading Broly to change his ways.
Well, a common theme is the exploration of Saiyan culture. Given that both Goku and Female Broly are Saiyans, fanfiction might delve into the traditions, values, and history of their race. Also, adventure themes are popular. They could go on quests across the universe, facing new threats and discovering unknown planets. Additionally, there's the theme of rivalry. They are both strong, so some fanfictions play up their competitive side, seeing who can be the stronger Saiyan in different challenges.
There are indeed some. I've come across a couple where the authors beautifully develop their relationship. They often play with the idea of how their different personalities, Goku's adventurous and friendly nature and Fem Broly's more complex, often misunderstood character, could come together in a romantic context. It's interesting to see how different writers approach this unique pairing.