Space Fuel has to go in Pirate or unclaimed sectors. Space Weed can go in Teladi space.
As for M6 class ships... pfft - I still love my Springblossom. Yea as you get deep in the game she lacks punch against anything larger than an M7, but between her speed, decent shielding, Starbursts in turrets for flak and 6 or 8 EM/AMs up front.... she is a dogfighters dream.
With the speed of a M5, firepower of an M6 and the maneuverability of a M3 - she is pure gold.
I strongly suggest that you look into the Marauders shipyard too....
At least until XTC is out that is