Hmm..I'm not the metals expert on the forum, but I can tell you what I know....

1. There isn't a particular metal sequestrant that we recommend. Mbar (one of the forum's resident metals experts), says that she has used a variety of them, and that they all work equally as well. Check and see which one is cheaper, because I understand that they can get pricey. You can read through the forum for posts by her, she addresses that question in other posts too.

2. If draining and refilling is a viable option for you, then it is going to be much easier for you to not have to fight the metals in the water for the life of your pool if you can remove at least some of them before they get into the pool. Keeping water balanced is somewhat of a chemical tightrope when metals are involved in the water, and it'll be much easier on you in the long run if you don't have to deal with it. It is also going to require regular additions of metal sequestrant throughout the life of the pool. So....if you can drain/refill without too much of a problem, and filter out at least some of the iron, then I would do so.

3. I'm fairly confident that you'll be aware of the presence of metals by the water quality--when the pH or chlorine get too high and there's not enough sequestrant in the water, it will start to turn brown/orange like it is now. So...there are metals tests out there, but honestly I think once you get this initial startup under control, you won't need one at home. I don't know how much they cost vs. how close you are to a pool store that CAN test for metals, but I would think you'll be ok without buying a special test for it.
We do recommend buying your own test kit that will test for the other water parameters, though--chlorine, pH, alk, stabilizer, calcium (not needed in your pool but nice to know the baseline level). Not only will your results be more accurate than the pool store's (fresh samples, consistent testing methods, etc) but it also doesn't give them the opportunity to try to talk you into buying hundreds of dollars worth of stuff that you don't need. (We'll start with calcium, move onto phosphate remover, and on to .....) The test kit we recommend here is the Taylor K-2006, which can be bought online at http://www.amatoind.com, http://www.spspools-spas.com, or http://www.amazon.com/gp/product/B00...SIN=B0002IXIIG . It's a little more expensive at the Amazon site, but PF gets a donation from them if you get it from that link. I know that the test kits can be a little pricey, but I guarantee you that it will pay for itself tenfold over just this summer alone, and is going to be necessary to give you full control over your pool, especially if you're going to be dealing with a metals issue.

Janet