Email--what's the relationship between email and browser / is that question too innocent?

Admit techno-challenged, so here’s the story.
I’ve paid an ISP for some 20 years so my email address shows “@theirname,” but now I’m getting so much spam and other crap–including messages supposedly from them–that I want to close the account. I believe they “use Google servers” (whatever that means), so it’s not clear to me whether there is any benefit to sticking with them. Here’s how little I know about it: (1) HOW CAN I COLLECT ALL THE EMAIL I’VE EVER SENT/RECEIVED (ON THREE ADDRESSES) SO THAT I CONTROL THEM, CAN BROWSE THEM, CAN DELETE SOME AND CHOOSE WHICH TO KEEP–BEFORE I SEVER THE RELATIONSHIP? (2) HOW CAN I COMMUNICATE TO THE REAL PEOPLE I WANT TO CONNECT WITH THAT I HAVE DONE THIS? CAN I KEEP ESSENTIALLY THE SAME ADDRESSES? My! that sounds like i have no knowledge at all --and possibly I’m just intimidated . . . . but here’s the thing: seems like microsoft and google are controlling all our web use anyway. The computer is running Windows 10 (which we hate) and if we are not careful --say, we follow a link in an email–we end up getting stuff from Bing and/or Edge even though Brave is our preferred connection and we do not ever use any “microsoft account” for any purpose. Of course email is not secure, but what we want to do is dump this ISP and its intrusion WITHOUT necessarily allowing any more intrusion than microsoft or google is already making. Thanks. best regards from the 1950’s . . . (feeling dumb)