What is the oil capacity on Honda shadow areo 1998, and can I use regular motor oil

You will need 4 quarts of oil. The correct amount is between 3.5 and 4 quarts. Use only JASO MA certified motorcycle oil. 10w-40 for cold climate 20w-50 for warm climate/touring. Do not use oil that is Energy Conserving it will shorten the life if your wet clutch and transmission gears(wrong additives). Synthetic oils will help your cycle run cooler and shift easier. Be sure to change your filter and purchase a spare drain bolt washer. A K&L filter wrench ($10) is also a useful tool if you plan to do your own oil changes.