If I play CW, which tanks should I be aware of?

I'm in the same boat as you. I wasn't a fan of true vision and I think this mode splits the player base. I haven't played  a game yet, and outside of hearing about the silver earnings, I really haven't had a desire. I currently have 52M silver so no rush to play it just for the silver.

Oh the Object 268 is mean in this mode. Most things can only hope to do 200 or 400 damage in Era 1 but meanwhile you can abuse True Vision and slap a tank for a third if not half it's health!

You're always top tier thanks to the era based matchmaking (top era 1 tank), so your threats? Your real threats? Other 268's!

I am not a fan of true vision, but the NM 116 from last season is very fun to play in cw. Watch out for them on the other team, they can take a lot of punishment, more than you might think.

How do the era 1, 2 and 3 things work?

If you want to be the dominant tank in Eras 2 and, you'll want to go up the Eastern Alliance line.
The TD part of the line will be more enjoyable getting there, bypassing the meh T-54, Obj 165, and T-62.
The T72-Av is top dog in Era 2. The T72BM and BU dominate Era 3.

What you would think of as heavy tanks are actually now MBTs. Heavily armored, big fast gun, and very fast. The heavies can literally run down most of the CW light tanks.

ATGMs are something to worry about if you are not in a T72 with ERA armor.
They do high damage and have the potential to one shot a tank. These start showing up in Era 2. The Mediums in that Era are very susceptible to being ammo racked by an ATGM if you are not careful.
They are mostly carried by certain Light Tanks, but the from the T72-AV and up also have ATGMs that fire from the main gun.

Another fun item, especially for the TDs is a piece of equipment called "Enhanced Zoom" This gives a much greater zoom and on some maps you can literally see from one edge to the other.