Is it possible for me to reach Lost Belt 2 (jp ver)

London to Lostbelt 2? Hell no, even with walking cheatcode Summer BB and Skadi, you still would have to face the cheat bosses of Camelot, and some hardas material of Babylon (like Quetz, who takes 0 dmg from good alignment servants and half of every1 else sans Nero Bride, Herc and Zerclot, so bye Gil and Jeanne; or the multiple constant NP full bar Zerc-Ushis).

This event will have a rerun, like the other Halloweens, in about a year, do the rerun and you're good.

Still, some events (GudaGuda 3) need Solomon completed, so, do try to dash a little more in the next months.

Sure. I also started at the anniversary and I finished Part 1, mostly relying on supports. It should be even easier for you with Summer BB and Skadi. For harder fights you can always use Command Seals (you have 17 days until the event so do the math).
My advice, if you REALLY want this: dedicate a couple of hours every day to this (so you don't burn out) and start looking for some friends while you trudge through London and America. Look for Euryale against Gawain, a good Saber against Lion King, Jack vs Demon Pillars and Ozymandias, etc. Raise up your Mash and Georgios so they can tank for you.
Just in case, remember that you don't have to play through Epics of Remnant.