Don’t think I’m trying to start crap with this comment… I’m not.
A,
Your welds look cold in most places. Which means lack of heat. Therefore, lack of penetration.
B,
Using flux core wire with a shielding gas isn’t a bad thing. It’s actually far superior to normal MIG and flux core without gas.
And you always drag flux core. And push with MIG.
However, unless you are very unfamiliar with the dual shielding set up you just stick to either MIG or flux core. It will be much easier.
Actually… You should stick with MIG as it is better to body work. There’s no flux to get stuck under the paint and hold moisture.
C,
Anything with flux core will tend to burn hotter. So it takes more fine tuning to get the machine set up right.