1.) You need either the jump gate, or a ship with a jump engine. If it is the ship then the limit on what size ship can go through is the size of the ship mounting the engine. If your jump engine is good for ships up to 6000 tons (120 hull size) and the mounting ship is 5000 tons (100hs) then the ship size limits what can go through.
2.) When you get there you will see the system bodies. Unless your passive sensors are huge, and there is a large population you will not have a clue about any inhabited planets, unless of course they are picketing the warp point.
Hope that helps you
Brian