At this financial level, it’s insanity to be fluting around on the internet or contacting Revenue for guidance. Engage with a decent sized tax firm and get professional assistance ASAP.
This +1
The only contact you may need to make with Revenue yourself, is if you still haven't engaged a new advisor, to explain that you've had issue with the tax advisor you had engaged letting you down, and need additional time to make a qualifying disclosure.
The importance of retaining the benefit of a "qualifying" disclosure cannot be overstated - based on the amount involved, if you don't make a qualifying disclosure, you will find yourself on the quarterly list of tax defaulters, which could impact on your business / career, depending on what field you work in.
Additionally, and possibly more importantly to you (depending on how you would feel about your name and address being published in your local newspaper as a tax defaulter), is the substantial difference in the amount of penalties you would be subject to.
You have said above that the current level of intervention is a Level 1 intervention - if this is correct then you can still make an Unprompted Qualifying Disclosure, which would mean penalties in the range of 5% - 10%, compared to 20% - 50% if you're making a Prompted Qualifying Disclosure (which would be the case if Revenue have notified you of a Level 2/3 Intervention).
So it is imperative that you act promptly to ensure Revenue know that you are working on a disclosure, and that they don't escalate or that you end up statutorily time-barred from making a qualifying disclosure.