These questions have been answered in one of the multiple other threads on this subject, but I realize the forum search function is "inadequate" to put it mildly.
If you're still seeing the Fee Rate then you're using a very old version of the wallet, it has been removed. Anyway it is the rate at which an asset, USD for example, can be converted to BTS for the purpose of paying transaction fees.
The margin call price is the price below which margin orders get margin called.
There is no shorting in BTS 2, only borrowing from the blockchain, this is called opening a margin position. You can then "short" the borrowed asset by selling it on the open market if you want.
If you look through my post history you'll find some other threads on the subject of margin orders.