It's probably best to recharge the bigger portion of this during Ino Flower event, so you get a good ninja right off the bat and make sure to not recharge 30k in 1 day, but spread it throughout the week so you get advantage of daily recharge rewards. As for spending ingots:

- monthly cards, jonin medal, extra convoy

- froggy event (it will take like 16k ingots to do full i think?)

- command flag in shinobi feast event (at least 1, and on multiple days you can win gold treasure tool essence with it)

- 3x daily hammer in myoboku trial event

- a few magatamas during the 1st week is fine so you can be 1st place in ranking but don't overdo it because they're not worth the price in the long run

Definitely fire main, I checked the speed of early leveling and it was faster than lightning main, while it's also very good in most p2w lineups. Lightning main would only be better if you plan on getting Ronin Naruto during these first weeks (which would be quite OP so you can consider it). You will also get Iruka during server opening event so you can build a konoha-based team with whatever oasis throws at you during this time or whatever you get from recharging. Edo Minato/Kushina is a no-brainer but you can play around with other choices.