After recently getting fired due to my military service, and then starting a new job, is it worth it to go to ALC next month?

Its sometimes hard to prove why you were fired. Often companies know it can't be because of military service but hopefully you spoke with the folks over at ESGR. If you haven't, reach out immediately for their input. They aren't your finally stop but can get the ball rolling on some fronts.
As for your current employer, be very upfront with them. Hiding things causes issues and they'll find out eventually. Should you get any grief, it would be advisable to present them with a copy of the laws. While its easy for me to stay don't work for someone who isn't supportive or rather, I wouldn't, you need a job obviously. But have an honest talk with your employer, what your military obligation means for them and how it will effect you. Be sure to lay out your loyalty and commitment to them.

I would speak with ESGR, consult your COC, and if need be speak with your units JA about the issue. ALC isn't something easily rescheduled so that's an issue, OCS will take up some time, and your employer also needs to learn how to cope with orders coming up on short notice.

I got tapped 1 week of additional AT to assist with work and do additional training, it was very short notice. Thankfully my employer was able to adapt to it, that said my supervisor is prior Navy so I lucked out.

Yes, you should go to school.
Putting your military career on hold is seldom a good choice.
Most employers understand that you have military training requirements, so long as you give them adequate warning of upcoming events. Do that and you should be fine.