I recently downgraded to EB3 and filed concurrent AOS and I-140. If my spouse uses EAD, does it mean I get tied to EB3 for AOS or I can still move to EB2 in case that queue goes faster?

You can still move to EB2.

SSN is your identity in US. Need SSN for getting a phone, car, house, etc as well as bank accounts, credit cards and so it is pretty important. Not relevant in context of new H1B except that the visa officer might expect it given you had a past job visa.

Is it okay to monetize on a mobile app while on H-1B visa?

Canada PR doesn't further yor chances for US Immigration. US Immigration depends on your country of birth and not your country of citizenship.

Thanks for bringing this to my attention. I'm born & brought up in India. What do you opine about the rest of the points?