that welding is fish mouth joints, the welds also are perfectly laid and look to have good thorough penetration, your weld job looks like a bird pooped on the joints - some even look like the welder was not even wearing a welding mask - just got the stinger close enough and looked away.
btw - the pipes you chose look like water supply pipes from a hardware store. They wont help in a roll jail that you have made.
anyway - the chassis legs in the engine bay have been poorly welded at the bottom edge - this is not a good idea - get entire pieces fabbed in a way that it lays like original and spot weld it again to the car.
for paint in the bay - the oldschool american way is black, oldschool japanese way is primer paint, oldschool german way is body finish or dark dark gray.