This is all in the guide if you would read it.
Landspeeder sale is in the Mos-Eisley level. You will have to open up a door to continue forward and in the next area you have to build an AT-ST, take the AT-ST all the way back to where the door is and destroy the stuff guarding an area. Go back to your landspeeder and take it through the door and in to the area you just opened. Once in the area you will see an open area across from the car wash..just go in there and it will unlock after the cut scene
Max out stud counter is just what is says...max out the counter which is 4billion studs (the money you collect) this will be one of the last achievements you will get. Once you get all 160 gold bricks you can build the machine to get this.
CaD4: Oblivion (1250): Avatar: TMNT: Lost Odyssey(1050/1100); Timeshift (1250): Lego Indy: Fallout 3 (1350/1350)
Cloning Clyde, Carcassone, Uno, Puzzle Quest(250),
The Maw( 230), 3 on 3, DoD