I don't know about 12"s, maybe 10"s.
on the sportster seat look at the pics in the tech section and get one like those.  I think the year was prior to '04.
'97 should of come w/ a 145
yes, you can.

There is enough room for 5'' forward controls. I have a set of Ed L's 4'' forward controls, but I think he makes 5'' as well.

i think you will find the #4 washer od to big to drop in the pocket for the needle. if i recall you need a 3mm washer or washers.

Order Lancer's jetset.  It'll come with the washers and jets that you'll need.

that will be the diaphragm between the carb and body. be very carefull with that sucker, it is expensive. make sure to return it to its original position when putting it back together. some folks have had trouble getting the screw out that keeps the needle in place. make sure you use a proper fitting driver for that screw.

considering the PO informed you about this site it's very likely any necessary carb work has been done already. Having just finished rejetting Id advise you that if you're new to riding/motorcycles in general Id read this site until your eyes bleed before you go about changing jets. Its a PITA doing it the right way. Doing it the wrong way...ugh...I cant even imagine. If you do decide to mess around with jetting Id go ahead and order Lancers set from the site. Its $22 and some change. You seemed focused on the spacer mod in particular. The 4 washers that come with Lancers kit together are slightly thinner than the stock spacer. Id start with all four. Ride it for a while with a new plug. Asses how it feels as you're riding and check your plug after...50 miles riding it that way. Then remove one washer at a time checking a new plug each time. Or if you find it runs better with the spacer, put the spacer back in. As to the forward controls, Ed L makes up to 6" forwards. 4" is the generally accepted standard here. The 4" made a huge difference but i couldve easily gone with 6" controls. Im 6'2" with a 32-34 inseam depending on the brand of pants. I cant speak to the seat or handlebars.

bell9440 wrote on 04/03/09 at 17:13:50:

pretty simple then, clean out all the jets and ports, make sure the rubber is still good, replace anything worn/torn.  That should fix the mid-range.  A 1/8 to a 1/4 turn on the pilot jet should fix the backfire.  if not, check for air leaks in the exhaust and intake.  check how many turns out the pilot jet is, if more than 3 turns, there's a chance it may back out on the road.