If you select a system around 650 light years away from your position you will get an in range fuel reading allowing you to make jumps of that distance making things much easier on long hauls.
To get enough money to buy anything you want start at system Lave, sell your hyperdrive, buy a passenger's cabin, get a passenger, and then try to buy a cheaper ship. Frontier has got a bug, the money you'd receive if selling your ship to get a cheaper one is added to your credits, but you never get that cheaper ship because you can't give your ship away if there are passengers onboard. Repeat this often enough and you'll never have money problems during the game.
Go to any spaceport, buy a ton of rubbish (this seems to only work with rubbish), leave the station and then hyperspace to another system (that's for not being fined for illegal dumping). Make sure you are in free flight (you can't dump with the autopilot turned on, and we really are gonna dump something) and accellerating (for not being hit by dumped cargo). Now do the following: Go to your ship's inventory. You see all your cargo, and the last should be a ton of rubbish. You also see the buttons for dumping the Cargo. Look at the rubbish button, imagine there was one more button below that and click right there. You just dumped cargo that you haven't loaded, and your ship gained one ton of space.Do this as often as you want, but be prepared that dumped cargo might damage your ship.