The minimum mass that an object would need to initiate deuterium fusion in its core is about 13-14 times the mass of Jupiter. At that point it would be a brown dwarf star. The minimum mass to initiate hydrogen fusion is about 80x the mass of Jupiter. At 2x the mass, Jupiter is well below both limits and would not become a star.

As for the gravitational effect of doubling the mass of Jupiter on the remaining Solar System bodies - of course it would have an effect. Jupiter was (probably) the first planet to form out of the original Solar nebula. At double the mass, it would have had an influence on a larger area of the nebula, therefore pulling in more of the gasses. This would have a greater effect on the formation of the other gas giants. Exactly what that effect would be is up for you to speculate (or run your own Monte-Carlo models) on.

Jupiter is also cited as a major influence of the movement of the planetesimals which formed the inner (rocky) planets. Doubling the mass would certainly change that influence. Again, feel free to run your own Solar System simulations to figure out how that affects planetary formation, but the end game is that the Solar System would be different.

I apologize in advance if I am making an incorrect assumption, but judging by your writing, you are not a native English speaker, so aren't an American (or UK, Canadian, Aussie, etc.) citizen. Every country with a manned space program recruits only their own citizens (so far) as astronauts. NASA astronauts are all American citizens (some are dual-), so any advice for NASA would be for Americans only.
If your country of citizenship is Canada or part of the EU , you can take a look at the CSA or ESA (respectively) requirements (which are pretty much the same as NASA's). Russia, and possibly some of the former SSRs, tend to recruit from the military, so you would have to have a successful career in the Cosmonaut Corps to be selected to fly a space mission. I believe that China has a similar military tradition (although that may change with Tiangong). The Indian manned program is selecting from their Air Force.
Finally, if you are not a citizen of the US, Canada, EU, Russia, China, or India, you would need to pay your own way to space, which can be as cheap as $450,000.

You might need to do some re-evaluation of your base assumptions.

1. Andromeda is roughly the same size as the Milky Way. At least to the extent of our measurement margins of errors (ironically, it's easier for us to measure Andromeda's mass than the Milky Way's)
2. A typical satellite galaxy has a mass of about 10 million Solar Masses. Milky Way (and Andromeda) have about 1-2 trillion. To double the mass of the Milky Way, it would need to absorb about a 100k dwarf galaxies. There's only a couple of dozen.
3. Astronomers have mapped the nearby universe, and we know where the nearby galaxies are - There aren't enough to substantially change the next few billion years of galactic evolution in our neighborhood

As for your theory, well it's...different. Galaxies do merge, and the merger process does disrupt their shape - but we really go know how to model these mergers, and the description of the future of Andromeda and the Milky Way is pretty well established.

(Edit: Changed some of my points to better address OP's "theory")

Tom Wolfe's "The Right Stuff" is a favorite of mine - It's mostly about the earlier Mercury astronauts (many of which were also Apollo astronauts), but it's written in more of a prose/story format than a dry recitation of facts.