go to Sportster forum at http://xlforum.net/vbportal/forums you can find a lot of answers to your questions
One down, four up.
under the seat
modern Sportys hold 3.6 quarts
Front 36 Rear 38
most 2004 and later 1200 use 91. But check your owners manual. Don't ask the sales man, ask the mechanic if you must call