Soldering is preference, but I do not solder mine. I have three VCA earrings and never had issues.
I do not like the fact the posts are permanently stuck in the earring. I don't sell my jewelry, but in case you do, as food for thought... some buyers may not want them if they are soldered, fearing they are "altered/fake" and not original.
Yes, you can unsolder, but that means the jeweler has to heat the metal to take it off or they may clip it and drill it out (not sure how VCA does theirs).
My motto for jewelry is the less you mess with the actual metal (e.g. resizing, polishing, soldering), the better.
That's just me though.
On your adjustment, yes... take your time. I had to send my Lotus earrings in three times, but it's worth it to get it perfect.
And yes yes... you are smart to remember the tension space you like!
My SA has it written down in my profile "client wants 4mm ear clip opening" so it's a no brainer when I buy earrings and have then adjusted.
You'll love your earrings! Frivole is my favorite of all time! Congrats again!