Hi SDrake!
Run a stringer bead for your root pass. I use a 1/8" dia. electrode with an ever so slight side to side motion (not really a weave but more like an inverted or upside down "C" motion) so that I get good "wetting action" (fusion) or "washing" at the toes of the weld without producing undercut at the bevels or LOF (lack of fusion) which in using E-7018 will produce slag inclusions by the toes of the root pass.
With E-7018, the flux coating is not producing anywhere near as much shielding gas as compared to other flux coatings found on SMAW electrodes so, holding your electrode closely (proper arc length) to the weld puddle or molten pool is critical in preventing porosity especially within the throat of the weld. Always keep the puddle on top of the slag and watch for the molten slag to run down the sides of the puddle and form a pattern of solidified droplets of slag on top of the axis or centerline of the weld face. If the solidified slag droplets are either to the left or the right of the centerline of the weld then, your work angle needs adjustment. A consistent pattern (size & location) of slag droplets
can tell you alot about what's underneath with respect to work & travel angles, travel speed, arc length and so can the color of the slag cover tell you whether or not you're welding with too little or too much current.
Also, use a flashlight and shine it on the toes and where the restarts are because the slag color (especially little inclusions or pieces) can fool you if your lighting is'nt adequate. If you find any slag that was left behind after wire brushing then see if you can get a hold of either a pointed tungsten or better yet, a piece of band saw blade to scrape out any slag that may be either trapped or left behind from the initial wire brushing. Remember that this slag is also very soft and the band saw blade is sharp so wrap some duct tape on one end so that you do'nt shred your gloves while you're cleaning!
Before you run your next pass and also on the next and every other pass, MAKE SURE THAT YOU CLEAN IT REALLY WELL!!! because if you do not, you'll end having discontinuities that'll total up beyond what is acceptable within the specified criteria or a defect that'll reject the coupons!!! You do not want that to happen... Be patient!!!
This is just my opinion but as an instructor, if one is just starting out with their first certification, I would'nt recommend to my students to use a triangular weave technique for the root pass when welding vertical up (3G) with E-7018.
I would instruct them to form a puddle at least three times the diameter but, not more than that of the electrode so that they can fuse or wash properly at the toes on to each joint member's bevel. Keep the center of the electrode on the centerline of the joint as much as possible.
Usually, only the more so called "experienced" students use the technique which you described and some are successful although, some are not!
Ultimately, if your toes look good, there are no slag inclusions, no LOF or porosity and your restarts are sound, you should be okay because it's normal to have a slightly convex face profile on the root pass when one is using SMAW with E-7018. Also, make sure that you have the proper root opening! I think you should be fine but, only the DE or NDE test will tell you for sure if you have to make some adjustments.
So cut the coupons and let us know how you made out! Good Luck!!!
Respectfully,
SSBN727 Run Silent... Run Deep!!!
If you are able to, saw the coupons in 3/8" wide strips across the plate perpendicular to the joint and see how your root has turned out. Pay close attention to the toes like SS has mentioned. Bend the strips and center your bend over the weld and see if anything opens up. This will show if you have entrapped slag or have LOF at the bevel faces. It may look clean when cut, but the bends will show any LOF at the groove faces. 
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