Loctoday,
I have a 2000 Civic EX, which is very similar to your car. I have successfully installed the following Si parts (OEM Honda) for my car: 13 mm rear sway bar, 15 in aluminum wheels, 195-55VR15 tires, leather wrapped steering wheel, mesh grille, and factory body kit (lip, side skirts, rear lip).
I also installed the Si's leather wrapped shift knob, however this requires you to purchase the Si shift lever boot, as the EX boot won't "clamp" on to the Si knob.
Also keep in mind that additional hardware (such as screws, clips, nuts, etc.) will need to be purchased if do choose to buy these parts. Since it is possible, though unlikely, that there may be some differences between the 2000 and 1998 bodies, you may want to check with the Honda dealer before you buy, so you don't get any unpleasant surprises.
Lastly, if you have the stock air intake, then do NOT buy the Si strut tower brace because it won't fit right (the stock EX intake tube has a plastic resonance chamber protruding from the top of tube which will interfere with the bar).
I hope this helps you, and good luck on your project if you decide to embark on it.