I think you are doing great!
With each flavor I'll take 5-6 10ml bottles and I always start real low and go up.
Say 1%, 3%, 6% on up (which way I test depends on what company as some I just do in drops).
And like you said flavors from different vendors vary in strength (even within their own lines). TFA vs CAP vs FW vs FA vs INW vs FLV (and all the others).
With the Flavorah flavors I do those in drops just because their flavors are ultra concentrated (super strong) ---> again I'll take 5-6 10ml bottles: #1 = 1 drop; #2 = 3 drops all the way to bottle #5. I do similar with INW and FA.
I just like to start as low as possible so I know what a flavor is like and then I take each flavor to the "tipping" point or where it no longer tastes like what is supposed to. I make detailed notes at each level of a flavor cause those notes come in handy when developing a recipe. Also I never use nic when I test flavors - just base + flavor.
When SFT I only do one flavor at a time and usually just one a day. I've found that works best for me. YMMV
I switch to vaping unflavored a day before SFT just to "clear out" my taste buds. Again, just works best for me.
I would say through trial and error figure out what process works best for you cause in the end it's
you who matters the most!

You are already well on your way!!!