Moving email offline

I have a gmail account with many year's worth of email that I want to move offline. I don't want to transfer it to another account because I'm not comfortable having the information out there.

What's the best way to pull down my email via IMAP and store it offline in an email client for long term storage and management? I'd still like to have it accessible alongside my other inboxes so I can search through it, etc.

I'm thinking I can add my gmail account to Thunderbird and then once it syncs with the account I can just drag all the online folders/email to a local/offline folder.

A few questions about that method:
1) will it work?
2) is thunderbird the right software and format to keep my email in for the long term? I have a few old work pst files that i keep encrypted but I never need to access them. If I ever do, pst is so common that i can import it into most email clients. Can I do the same with the thunderbird format or should I look into a different format?
3) I use apple mail client and it's very nice, but it seems very proprietary. Not sure if that's a good format to store email in for the long term.

Thank you for the help. I'm finally breaking away from google for good.

 

Can't remember exactly what I did but I used TB a little while ago to do more or less what you've described and I had no problems. Id recommend perusing through all the settings. I did mine from a web based account which is now assigned to languishing on the back burner.

I like to watch a few YouTube clips and right now Im experimenting with how much I can get away with before google put the screws on.

I just CANT BELIEVE how many sites want you to enable google this or google that to get even reasonable functionality.