Question 1 - Back
Although placing 7c in the back row eliminates your chance of any royalty opportunity in the back, pairing the 7's opens up a new door to Fantasy Land with this setup. All you need is another Q (front), A (middle) and 2-pair of better (back) with seven cards left to draw.
Also note that all the 8's are already exposed, so your chance of catching a straight here in the back row has diminished dramatically since you will have to look for the bottom end straight with 7 high (forcing you to catch the last 3 in the deck).
Question 2 - Middle
Placing Js in the back row may look like the right choice, but it will actually guarantee a foul hand, since all 6, 8, 2, A and spades are exposed already. Although a slim chance of survival, you still have one more 4 in the deck to hit your full house on your last draw (14.3%).