Give your players some freedom but don't let it get beyond what you can control.
There is a lot of stuff online to get you started on a subsector, if you don't want to create one youself. And if you don't want to go with Spinward Marches, Solomani Rim or another well documented area (where you have to buy a sector book), either go with a pre-mapped area, with no published material, or just make up something yourself.
Definitely go to Freelance Traveller to take a look at a ton of good material. NPCs, adventures, settings, equipment and ships. All the sector books are pretty good to great, if you want to buy material. Solomani Rim is excellent.
But remember the free ranging nature of travelling can get out of control pretty fast. You write up an adventure and give your players a ship and boom! They decide they want to meet some Aslan, or overthrow the Emperor, or something else that totally ignores your well crafted ideas. Don't railroad them but make sure your premise is understood. Talk to your players - do they want to be mercenaries? Merchants? Explorers? Do they want to save the universe? Its easy enought to start a campaign on any of these ideas.