I'm not clear as to the description you gave correlating to the pictures you posted. It appears the picture 2 & 3 are the same picture.
Anyway, picture 1 that shows a stacked fillet look good.
Picture 2 (&3) the fillet weld has bad undercut on the "bottom edge" as plate is oriented. If that was a vertical "up" weld, then it is an indication you are not loitering at the edges long enough to deposit weld. Think 1, 2 sweep when you stick weld. Whatever you do to one side, you must do to the other (metal thickness being equal). Sweeping across the middle allows the puddle to fill itself in, you're not trying to deposit weld there. If you do so in a vertical "up", you will get sag and drop gobs of weld onto your toes or other Gentlemanly parts.
The stringer beads look very "cold" to me. I would say you need to increase the heat, and slow your travel speed down. When I weld stringers, I almost am only "feeding" rod and never want to feel like I'm pulling the puddle. This insures that I don't undercut/underfill the weld, don't stretch out the bead, and get full penetration.
Remember, Stick welds are completely about strength. Great stick welders make their welds look "nearly as good as" TIG/MIG, but they focus on insuring a strong, consistent, risk-your-life weld. Do that, and the pretty weld part takes care of itself.
That's my impression of the pictures and I hope you will find it positive, and constructive input.