My recommendation is to use your lugs you have now for practice before doing a main triangle for real. With instruction, students can really make brazing improvements with some practice. I've taught hundreds how to braze and almost none of them could have brazed a lug decently without practicing first. You have to avoid rookie mistakes like not bending the silver straight enough (or it takes more concentration and coordination to keep it where it belongs as it melts), at the right angle (same reason as #1) and don't relax your hand holding the brazing rod to your side because it takes too much time and thought placing it in position when the joint is up to temperature. Most beginners can either keep track of their filler rod hand movement or their torch hand pattern but they can't do both at the same time until practice allows for some muscle memory to take over.

The primary issue learning to braze is operating both hands independently of each other. I constantly remind a student to keep the same flame to joint distance and/or keep point the flame towards the center. A normal person's mind can only keep track and respond to half of what they should. Practice becomes your way to get past rookie common mistakes.

So of course I'm going to suggest starting with simpler practice brazes to get used to moving both hands like you should. Once you are past the awkward stage, you can start with lug brazing, I'd recommend using the lugs you have on a complete front triangle so your practice and real frame can be held the same way as you are brazing. You will learn a lot. I'd also recommend adjusting the design of your practice front triangle to better fit the angles of the lugs you are using. Don't think of it as a frame to ride. Use .035" wall straight gauge tubing from aircraft suppliers.