I have not which is why I posed the question. Also wouldn't you only have 3/4 members of your team as an element?
Main character plus three others are the front, subs is two others.
Oh right, I didn't really answer that question, my bad.
So the differences in starting now or a legfest is how much you're willing to pay/endure.
Starting during a legfest and rerolling for something you want then start dashing/waiting for the next surprise ticket would be the best value for your buck/time. Going this path, you're looking at least another three months before a surprise ticket may come back but you'll be almost 100% sure you're getting what you want and not leaving it to chance without taxing your sanity. If you decide to play now, you'll have to suffer lower SSR rates and with no limited characters in the pool, it'll be fairly taxing on you having to make 20+ accounts before you even see one SSR, never mind if it's something you don't want. You may even just give up and take a non-SSR start but with a start dash/ST here, you'll at least get two units you want and can start playing the game right away, if that's important to you.
Sorry I can't give you a clear cut answer on this, this is just too sticky of an issue for me to pass judgement on since I don't know how willing you are to whale or if you value not throwing money at stuff.
tl;dr:
-Are you a whale/don't care for limited characters start dash?
Start now, pick up the ST/start dash. Buy whatever the heck you want
-Are you willing to dip your feet in once in awhile/don't have the patients of a saint for rerolling?
Start during legfest, start dash when you feel conformable with the game/whatever team is forming.
-Can you get someone's decent rerolled account?
BEST OF BOTH WORLDS. Get something decent and ST/SD open to you.
Save all the free 10-rolls you get from start dashes/skins/surprise tickets for Legend fests, and to a lot lesser extent, rate up events for a limited character you
really want. I'd only do that if you were 1000% sure of what you're doing and the chances you're taking.