Almost all token support by myetherwallet, you can check the tokens you have there, because myetherwallet is arguably the biggest wallet
Yes, you are right. I agree with you
not all tokens are erc20 based because there were some tokens that is only based on waves and that simply means not all tokens are supported by mew. however tokens isnt the only one that can be put on mew because altcoins , bitcoins , etherium can also be applicable thru it.
Overall , mew or myetherwallet is a good wallet when it comes to storing alts and tokens but keep in mind that mew isnt the safest wallet that you can get on the web as it is mostly prone to attacks and hacks due to poor security.