Spring Water Collection and Distribution

Here is one for you guys to chew on.
I am developing a spring to supply water to some rental cabins. I have a new cabin built near the spring and the pump will be powered out of this cabin. Eventually I would like to supply up to an additional 3 cabins(4 total within 5 years). The cabins are small and will only accomodate couples(shower/toilet/sink/lav). I suppose I will need less than 5gpm per cabin. I have a 1700 gallon HDPE cistern that I will bury just downgrade from my spring source. I have buried a 1 1/4" HDPE main from the tank location toward the eventual cabin locations. There is a 3/4"(200') branch Teed off of the main to the existing cabin. I buried a wire with the pipe to power a submersible pump in the tank. My intention is to have all components inside the tank for freeze protection. Vertical elevation from tank to first cabin is about 75'. The branch tee is about 250' (linear) from tank. Additional cabins will be appx. same vertical elevation and up to 500' apart.
Questions:
What size sub pump do I need?
Do I need a flow sleeve?
Can I mount the pump horizontally?
Can I put a bladder tank in the cistern to freeze-protect it?
Can I modulate the pump power with a pressure switch in the first cabin?
Could I put the bladder tank in the 1st cabin or does the 3/4" branch size preclude this?(I think it would work untill other cabins were added?)

I was all set to buy a grundfos sqe until I found out the transducer is not submersible! (outrage)
I also have questions about the spring catchment construction, but not sure that is appropriate on this forum!

Thanks in advance for any help guys!
You can see our prexisting ops at www.bigrockcabin.com
(I am especially proud of the plumbing

I don't know where your located but I would check to see if there are any local / state / federal water regs. that will apply to you if the cabins are open to the general public.

I liked everything except the 3/4" line running 250'. Is this the line that will feed all these cabins? If so, you won't need much of a pump since squeezing 10 gpm through a pipe that small already causes you a 28 lb pressure drop.

I don't think you can get a bladder tank to go under water without a very large anchor.

bob...

I would filter and disinfect any spring water serving customers in rental units. The storage tank makes it worse because they are never adequately sealed, get insects inside, and grow algae.

I install small water systems supplied by lake and spring water. I filter the water going into the storage tank with a good cotton string-wound filter. The water going into the tank is chlorinated.

Then I use a 1-micron-absolute filter from the tank to the users. http://www.harmsco.com/uploads/pdf/harmsco_polypleat_catalog.pdf

The last thing you want to hear about is someone going home and getting a case of crypto or giardia.

I have used two pressure tanks for long distribution lines. One is at the pump with the pressure switch; and a second toward the end of the line with no switch. The second tank provides water for two-way flow and reduces the pressure changes for the spikes when someone turns on the water.

If you have only one tank at the source you will get terrible fluctuation in pressure when someone along the line uses water. The users at the end are affected the most.

If you look at Franklins pump manual, they insist on a sleeve for cisterns and wells that top feed the pump. In horizontal app's the bearings are greatly downrated, and they want 10 or less starts per day.

Seems like a fabricated flow sleeve that is sealed to the outlet pipe would allow the pump to stand up and slots at the base to draw from the bottom. I don't know if thats ever come up here or not.

but If you go with a small HP motor, and a deep tank, then that distance of pump screen to motor bottom is small enough ignore and to call settling area for sediment. I would definitely stand the pump upright - although many seem to get away with the horizontal installation.