#1
Should i buy amp or audio interface for practicing
I already use Rocksmith USB cable and AT4, GR5
im interested for Marshall Code 25 and Focusrite  Scarlett 2i4 or line pod studio ux2
#2
I wouldn't advise the purchase of Marshall Code. Out of these probably the Scarlett only.
Personally though I would go for higher quality interface, possibly Audient as it is just a few $ more, or would go for a completely different solution, like Laney IRT Studio or IRT-Pulse recording preamp.