All your other questions seem to have been answered, but I could suggest an alternate routine for you.

It's a triangle, meant for endurance swimming. Assuming your pool is a standard 25m lap, start off with 10 laps free, 8 back/breast, 6 breast/back, 4/2 butterfly. 30s rest, then you go the other way (2 butter, 6 breast, 8 back etc). Do as many cycles as you can do in an hour. Finish off with 10 laps of choice, I recommend breast. Butterfly should always (imo) come after or before an intense style like butterfly, as to me personally it's always been a buffer to catch my breath.

The first few training sessions doing this will leave you exhausted, but it won't take long to build up massive stamina, at which point you can up the number of laps for each style. My peak performance was around 17 when I did 18f->16ba->14br->10bu->br->ba->f, started off a bit before you though, now I do 2 laps extra to what I originally said (21). You can, of course, do your own number of each, in your own order, and you can phase out butterfly if you'd like.