Putting on weight before hitting the gym?
You wanna bulk you gotta put on wait while lifting.. And yeah I think you should def bulk up do some reading first.
Try to keep your arms still with only lower arm movement( elbows shouldn't move around) less movement in the shoulder. This will iscolate your tris alot more.
Keep your body inline when extended but don't go too far, also try to arch your back a bit once your have fully extended.
You can try either placer your arms across your chest...
For the barbell row try using a lower weight in order to practice the contraction of the lats. Focus on using your arms only as levers while contracting and pulling with your lats.