Donimo,
The tubing is marginal in terms of cost. Since you have 100 ft of it, you may try and ebay it or post it on sale on here. With the funds from it you can buy more than just the tubing size you will need for your wc setup.
I myself have recently started the WC due to noise from the 9800 GT video card and cpu and motherboard fans. In terms of noise, it was GPU > NB > CPU. So all 3 had to go. At the end it cost me about $1100 total. Though you could prolly go about $400 for one of the kit that Linus has made available on NCIX or on canadadirect.com.
Alternatively, keep an eye on the Buy & Sell section on this forum, you'll likely find some parts that will work for you.
In terms of not making mistakes, the biggest thing I learned was to make sure the tubing and fittings match. Plus the fitting actually have enough space on each waterblock items. I went compression fitting which are quite large in diameter compared to standard fittings. This caused a fair number of waterblock items to not being able to fit them. You can take a full review of my worklog
here.
Good luck on your project!