Gas Price is amount ether will be use for your transaction per unit of gas. Mostly we will see a gas fee as Gwei. About gas limit is maximum gas you need to spent for every transaction. In standar you will see as 21.000 gas limit for ETH transaction. For token transaction it will different, you need to check any lowest gas limit for that token. Don't make a gas limit lower than minimum for token or you will be spent a fees while your transaction will be fail. You can make it higher than minimum in case that need more gas to send. Let say if minimum gas from token 150000, you can make as 300.000 for gas limit. No worry about the number, if your transaction just need to use 150000, the rest of your gas will be back to you.
I have never been conscious of this. I didn't know that excess gas limited is always sent back to the sender. Well, that is a good observation, because sometimes, I get conscious of that and try as much as possible to reduce it.Yet, I think most tokens can use as low as 60,000 gas limit, even with the lowest gwei for the network at that particular time, except when you are sending zero Eth, which is mostly applicable for self drop airdrops.
