"Here there are a lot of poor people."
Translation:Aquí hay mucha gente pobre.
"Gente" is feminine not masculine so "muchas gentes pobres" is accepted as an answer although generally statements like the example are looking at people as a singular unit (a group) instead of individuals and so will typically (though not always) be "mucha" not "muchas".
I believe that "pobre gente" would mean "poor people" as in "those poor, unfortunate people," while "gente pobre" means "financially poor people." When you're talking about a "new book" you say "nuevo libro" to say that the book is new to you. So say you bought Don Quixote. The book itself isn't new, it's very old, but it is new to you. If you say "libro nuevo" however it means that it's a newly written book, new to the entire world.
That's a good question, even as a spanish speaking person myself. Those words mean basically the same thing, but "personas" encompasses a broader field of what a human is (a group of humans); "gente" refers to a group of humans who shares some common traits, such as a tribe. It's very common to use the expression "mi gente" to refer to people who belong to your same culture, region, or shares specific tastes/hobbies. On the other hand, it would be really strange to use "mis personas", as if a group of people belongs to you (the implications are even worse).