Thanks and some more questions

As you can see, the underbody is kind of rusty and the seller claimed he go offroad on sand and mud weekly.
Will this rust cause a lot of problem or it is curable?

After installing the lift package, what should be done
for track bar and control arm?
Since the ground clearance is higher, I assume that the track bar need to be longer to allower the body move a bigger distance virtically
As for control arm, I thought if bigger tire is used,
there would be no need to change the size of control arm. Then what else need to be adjusted?