ERC20 Token Transfers – How to Add a Fee in Ether

Transaction fee on Ethereum is called Gas and is paid to the miners for the processing power they spent on the function call, here being ERC20 transfer(). Tokens on miner's level don't have any value and does not mean anything, rather than just a state change in a smart contract. Gas can only be the same coin/token that the blockchain is using to incentivize the miners, so here on Ethereum blockchain Gas is Ether.

To understand more of this concept you can read here: https://ethereum.stackexchange.com/a/62/3157

You don't generally do that. It's a matter of separation of concerns.

The OP didn't say exactly what the end goal is. A common scenario is a token contract and a crowdsale contract. Let each one do what they do and don't mix up concerns.

The ERC20 contract's job is to keep track of use balances and facilitate transfers. That's it. Anything beyond that is creeping beyond the concerns of minting/supply and basic accounting.

A CrowdSale would typically offer some tokens for sale at some (business rule) price. This "store" is "stocked" with merchandise (the tokens) and it sells, possibly buys in exchange for ETH. Thus, it has simple functions to accept Ether and transfer tokens that it has, and possibly a method to redeem tokens. It's not concerned with wallets. The ERC20 "minter" or "deployer" usually receives the initial supply and can safely store the tokens, periodically "restocking" the store as the tokens are sold.

Things will work out much simpler if the token contract is considered separately from whatever activities one might want to use it for.

Hope it helps.