You won't be sorry with the GEO reactor. I have one of the first custom large units he ever built about 5 years ago and it looks like I got it yesterday. Very well built.
As far as the media goes, I mut say that I have used everything in the market with the single exception of the larger Koralith media and the Rowa media. Price aside and if you use PO4 removing media in your system, when the reactor is dialed in they are all the same. I personally would never buy a Deltec Ca reactor for the single reason that it only works with a single media (Rowa) and I can't possibly see how being limited to a single type of media is a good idea. I also would never buy a MRC product again after getting several POS equipment pieces fromt hem. However, you are passed this point in your decision making.
After using the larger schuran media most recently, I simply switched back to FL crushed coral. The larger schuran media that was mentioned above by some is the same no matter what many different places call it. It is all imported by the same people (single importer in the country) and distributed to different places, which then name it what they want. Although it was nice int hat it won't turn into mush, it requires a lot of CO to attain the low pH at which it works best (6.2-6.3). For me that is not an issue, but for a lot of people that run low pH in their tanks to begin with this large acid load is not a good thing.
Solenoids and pH controllers are a waste of money in my book. I would spend my money elsewhere. As far as the regulator goes, you can get one very cheap off ebay. Look for home beer brewing kits and save a ton of money too.
As far as feeding the reactor, I have found over time after using just about every other method that tapping a line off a pressure rated pump serves the best and most consistant results over time. Whether it is your return pump or a close loop, it does not matter.