snip
I don't intend it to be mass people colonised. More proof of concept and mining.
snip

Considering you think all my comments are unrealistic, how exactly do you plan to colonise other planets ? Will we have some magic terreforming machine that will make trees/oxygen/fuel and water on one of these inhospitable worlds?
And there is the small problem of actually transporting say even a small number (I will pick 2000 humans - the minimum needed to keep any species going) people a few million miles. What are you going to get there with - 2 pints of water and 200 tins of beans.
And what would they mine ?
Iron, Titanium and magnesium on Mars or the Moon.
Maybe you think we will actually get to the speed of light in 3 or 400 years so we can get to the nearest earth like planet - because all the others nearby have absolutley no resources that are any use to us on earth (or ones that could be brought back easily)
And if we were stupid enough to send a team of humnas to a gas planet to 'collect' one of the gases - what would do then ? Orbit it in a big spaceship ? Or send a 6billion tonne gas liner back to earth.
Sorry, but wake up and see reality. This isn't Sci-fi - its our world, and you aren't going to see anything like that in the next 500 years. We've reached a limit to how far the human race can go - and the moon/mars is the limit (in fact, we might not even make it to Mars and back in the next 500 years)