RGB98 and all other color spaces describe the color gamut or range of their respespective spaces. On a Mac, (in your colorsynch folder) you can view the color spaces in 3D, and utilizing the "hold for overlay" (or something similar), you are able to overlay one space on another to verify and decide which space you want or need to work in. RGB 98 is indeed very large and very commonly used and is the right choice normally to set in your Photoshop preferences setup.
Gamut ranges indicate how many colors are included in the device specific hardware you're using the colors in. ICC profiles intend to translate various gamuts one uses in the shoot to print or publish process and Colorsynch is Apple's soiftware app that interprets (transparently!) the various translations in the process.
When you shoot an image, the optimum (unless you're only shooting for a client who will run off with your originals) idea is to shoot in the largest file size, widest color space and highest bit depth possible today. I know many wedding photographers shoot in sRGB and jpeg file format but they don't intend to make their images again and again in multiple outputs. You can always diminish or throw away information, but you can't regenerate it bigger (file sizes CAN theoretically be enlarged, but they are subject to interpolation algorithms and you're subject to somebody's interpolation -you lose control!- and therefore reduction of image quality). Further, there is really nothing you have to think about when it comes to Colorsynch, but you do have to make sure you have up to date ICC profiles for all your various devices, including, ideally, paper profiles for the papers you want to print to. And vendors make it pretty easy by usually putting them in the download package so you don;t generally need to go out and hunt them down. There is a typical exception- paper ICC profiles for the papers you intend to print on.
As far as Photoshop goes, you need to play with it for endless hours, but a great way to end run most of us who have, is to take a class with a pro photographer (not an illustrator or a "digital artist" as they will have you putting blazing purple rings around heads and over high pass sharpening everything rather than teaching you the basic-and subtle, powerful- uses of levels, curves and saturation controls.
FINALLY! Go out tomorrow morning and buy a ColorEyes Monitor calibration device so you WILL see the colors you're editing. They run about $150-$399 for the "good enough" ones.
Cheerio!