Yes, I think you should be able to remove liquidity but for that LP tokens should be in your wallet. So unstaking LP from SushiSwap will be a transaction you will need to make separately.

Regarding yields, I ain't too sure. I don't harvest so frequently. In fact, I haven't harvested so far. What do you do from your harvest? Are you selling them right away?

Yes you get block rewards on your liquidity but I think that is 1000 SUSHI on every block distributed to all staked LP proportionately.

Finaly, 5.073 is not your SUSHI but LP. You can login to your Zapper dashboard and check your actual SUSHI in the pool (I've provided the screenshot of my holdings from this pool only). The ratio of your ETH and SUSHI will change with every trade in the pool and 0.3% fee will be added to the pool. If SUSHI nos. are reduced then your ETH mush have increased. The product of these two will always remain constant + 0.3% fee.

Hope this clarifies a little. I ain't an expert as I'm also learning :)