Yes, get some mylar on the walls soon if you are growing in the area that you took the pictures. I am colorblind so i cant tell if your walls are white or not so i may be wrong. But i would put some mylar up anyway.
Throwing some tin-foil shields here and there are great, if your fingers are used to it. Personally, I spent years of my life making at least one tinny every day, so I'm used to working with tin foil hahaha but on the real, just to save money. From what I know, mylar wouldn't do shit from that distance with CFL's. Some well-placed reflectors might just make some more use of those lumens, which drop in count massively inch-by-inch, in comparison to HPS.
Definitely not required. Your plants look quite sexy. Congratulations, it's a girl