Immersion chiller build question

I am gradually putting together my gear for my first brew. I plan to do full-boil, 5 gallon extract and need an immersion chiller and a pre-chiller. My plan is to buy 50' of 3/8" tubing from www.coppertubingsales.com for $36 + $10 shipping, saving me about $10 vs. Home Depot. My question is should I make 2ea 25' chillers or 1ea 30' for the immersion and 1ea 20' for the pre-chiller, or some other variation?

Honestly, I don't really see much of an improvement with a pre-chiller.

I have a 50' IC that I use. What I do is about 10 minutes before the end of the boil, I start a big ice bath. I submerse a pond pump into the icewater and run that through my chiller. It's the same as a pre-chiller I suppose. It takes me about 10-15 minutes to cool a 5.5 gallon batch to 65-68F.

I plan to pump water from a series of rain barrels and then back into the rain barrels. If the barrels are empty, I will just use my well water and dump into the barrels. Either way, the water is not cool enough. The pre-chiller will be in the circulation loop sitting in a 5-gallon bucket but I won't bother adding ice and water until the wort temp drop starts to slows down. My research seems to indicate this is a good option, but ther may be other options.

I was having some issues with the summer temps of my water with my 1/2" 25' copper immersion chiller and I considered a pre-chiller as well. But I looked at a bunch of options (pre-chiller, larger immersion chiller, plate chiller, counter-flow chiller, etc.) and went with a $34 pond pump to pump ice water through my existing chiller. My logic was this ... My current immersion chiller worked great in the winter when my tap water was 48 degrees, I could easily get my wort down to 60 degrees. My tap water is now 72 degrees and I knew if I could somehow get my water down to 48 degrees or less I would be a happy camper. My ice water is a nice chilly 38 degrees, I be a happy camper!

So if you can build a pre-chiller pretty cheap then go ahead and give it a try. But I guess I came to the conclusion of why try and cool off tap water with ice water using a pre-chiller when you can just blast the ice water directly?

Here is the pump I bought:
http://www.lowes.com/pd_206234-70161-19032_4294857871_4294937087?productId=3020341&Ns=p_product_price|1&pl=1&currentURL=/pl_Pond%2BPumps_4294857871_4294937087_?rpp=30$Ns=p_product_price|1

+ 1 to the pond pump and ice bath. I have a 50" 1/2" copper immersion chiller and our tap water here in OH is running in the high 60's this time of year. So I have a splitter on the inlet side and cool with "tap water" until my wort get in the 100-110 degree range. Then I switch over to the "ice water". I also use a pond pump. Got mine @ HF on sale for about $16. It works very well in the hot summer months.

Here is the pump

Okay - I'm convinced to drop the pre-chiller idea and pump ice water after initial cooling with tap water. The HF pump cited by bad67z looks good. Now wondering about chiller size. Local stores only sell 20' and 50' rolls. The cheaper online stores only sell 50' and higher. 1ea 50' seems more than I need for 5 gallon batches but doable. Or 2ea 25' with one wrapped tighter and put inside the other. If I do this option, why not use a hose splitter and run a separate water circuit through each? Or I could just build 2ea 25' chillers and sell the second on Ebay to recoup some of my money. Thoughts?