there are approximately 138 ea per lb.
Screws for wooden porch floor should be at least 1" longer that the thickness of the floor boards. The 2-1/4" screws will work with 1 1/4" wooden deck boards but if the board is 1-1/2" thick, the screws should be 2-1/2" long. Stainless steel is a good chose in either #7 or #8. These type of deck screws normally have tips that do not require predrilling. I would suggest however that screws should not normally be placed no closer than one board thickness from the end of a board in order to help prevent splitting the wood. If this distance is not possible, predrilling will help reduce splitting.
No - not to my knowledge. These finishing screws are designed to sink into the wood and leave a small hole, which you can easily fill with putty. On exterior installations, the wood will actually almost close after being exposed to the elements. On my Cedar deck the holes closed significantly after a couple of rain storms.
They might mushroom , but might give you self sealing material to push in hole I had to countersink in fiber-cement Hardie trim boards
Yes, it does.
There are 138 screws.