> 1. Is it easy to set up the redirect from Gmail to the new account?

Yes super easy. You can do this using Gmail's filter service. However, many services will also let you log in to gmail via POP/IMAP (OAuth for auth) and fetch the email from your gmail for you that way.

> 2. When I send email from new account (custom domain), how are you completely sure it is not going to be on spam? I send unsolicited emails to people in big corps (journalist asking for interviews/comments, not spammy :-)

I guess it's hard to know for sure, but I've not noticed any problems with this when the underlying provider is a well-known sender such as Gmail or Fastmail.

You don't need to set up anything in Gmail either, Fastmail has Gmail connectors that pull all your mail and calendars and even lets you send email through Gmail from Fastmail. It's ridiculously convenient.

I have had Fastmail pull from Gmail for about 10 years just in case I need to log into a website I haven't logged into for ages. It just works. My gmail is abandoned save for the occasional password reset which flows through Gmail to Fastmail.

You point your domain to Gmail. Then when they ban you, you point your domain instead to the new place, like Fastmail. So it's not really redirecting from Gmail, it's just changing a DNS record.

On sending from a custom domain, your mail provider walks you through setting up a few additional DNS records (for DKIM, SPF) that allow you to send from your domain through their servers. They maintain the reputation of their IPs and so you get their good deliverability.

1. Yes, can't be easier 2. None of my emails have been flagged as spam.