Does Bakuman explain the life of a mangaka realistically? Is the way shounen Jack works the exact same as jump?
I'll highlight the main points made in this article by Justin Sevakis:
Well, the thing is, Bakuman. presents a very romanticized, very clean-cut, idyllic perspective on the "manga industry." And it works in that sense - it's goal, as a manga itself, is to make you care about the dreams of these young Shonen archetypes and hope that they will achieve all their hopes and wishes through hard work and many tough battles - but it is far from a realistic portrayal.
I'll admit that Bakuman. gets a lot of the specifics right, and it succeeds at presenting an otherwise dry, self-referential premise in an entertaining way, but it is far from realistic.
And, the other thing is, I dunno how many conventions you've been to recently, but take a good, honest gander anywhere around Artist Alley and you're likely to find several eager young artists proudly hawking their most recent Graphic Novel. Granted you won't see as much of this stuff at anime-focused cons like Otakon or whatever, but if you're ever in the vicinity of any all-purpose Nerd Convention near your home town, you'll be able to walk by dozens of booths rented by local artists promoting their self-published work. Essentially, there are a lot of people out there who are dying to sell their own graphic novels, outside of the manga realm.
Another point made on this matter isSource:
Jason Thompson referred to Bakuman as "a love letter to the manga industry done in old-school shonen manga style." He felt that while it can be "text-heavy" on the process of making manga, it is ultimately a "heroic story of self-improvement, friendship and striving to succeed."
As for your other question, Shounen Jump is pretty much the same as Shounen Jack and it was only renamed for copyright issues. As mentioned in an interview with Takeshi Obata, the mangaka of BakumanSource:
Ohba Sensei creates characters who have realistic personalities. When I draw them, I slightly reference real-life people that I’ve seen in this industry and exaggerate their qualities to turn them into manga characters.
The whole time I was working on Bakuman, I felt like I was drawing about my everyday life