@Rima is right, it would make your life much easier to use that tutorial and after you have learned his methods you will be able to make any car you want and slowly improve your skills
Well, it's hard to judge the accuracy of that truck without knowing what you're comparing it to. But regarding your other points... The flat matcap basically just shows you model without any shading, without any shadows. It's useful if you just want to check the silhouette of your model without being misled by shading or…
Well, I'm not sure why you'd need to use the lattice modifier here. And even if you did, that's a lot of subdivisions; will the model even have enough vertices itself for that amount of detail on the lattice to be effective on the car? I think you should try to just focus on modeling for now; ignore deformation modifiers.…