Would go with 360, why pay for more electric when not needed. All you need to do is add a 3 way valve so you can turn it on and off. one last note you can convert 380 to 360, you just need to get the bigger tubing and replace the inside piece where the tubing connects to.
If you are handy you could replumb your system. Using your main pump as water supply, plumb a new pipe where your booster pump went using a 3 way valve. Buy Polaris 360.
If there is concrete around your pool it wouldn't be easy to add an over flow.
I like to drain pools 4-6" below skimmer. I think they maybe worried about the step shifting, if that's the case you could put a water bag on the top step to prevent that.
You don't want to get water behind liner.
The piece of flex above the pump is not required. Yes you can put tablets in skimmer. You can blow out the lines by removing the backwash hose, and put the multiport valve in between positions. Yes you can remove the valve in front of the pump.
I have never seen cloged returns. Try puting pluges in the returns that are working and see if the other returns work then. Are you losing any water? What kind of filter/pump do you have?
I would get the water pumped off the top of the cover as soon as possible. depends on the age of the liner. You may be able to use a hair dryer to warm the liner so you can put liner back in liner track.
agree with Jason. Thats why I dont post often. A part like this should b what you need. http://www.amazon.com/Hayward-SP1082GV-Skimmer-Replacement-Automatic/dp/B004VTG7EE
You should be able to twist off the grey fitting. you can use a fitting like this http://www.acepools.com/product/2633/SP14953S?gclid=CJ6pkNyBob0CFQ2hOgodtlUA2
I do no not know this store, just showing a fitting that should work for you.
be very carefull you understand your system..its not worth couple thousand to dig up broken lines..in a pinch ive taken the shirt off my back wraped it around the blower hose, then put it in the pump, you will need 2 people for this. 1 to hold the hose in the pump and 1 to plug everything.
if you plug the pipe in the skimmer that goes the main/bottom drain, you will have to get in the pool and plug the main/bottom drain also. if that is where it is leaking. i had to do that to 4 pools this past year.