1 Stock /sachs exp to rebuild. Stock 260-300$ probably best to keep increasing bump and rebound each rebuld...
2 Kool, but does that include wiring harness and dme? Probably need those to do that conversion...? Legal, visually yes....need to be quiet should You do it. Not a monster advantage over the 03-05 motor but a bit yes, cant be detected unless You say something except for engine number of course...
3. It will be as fast as any 6 well driven. RACE CRAP OUT OF CAR>>>>

4 Gears in car woukd be great with new motor. Short gears are arguably better for what You have in it now. Never was convinced I didnt spend more time shifting with the short gears vs being able to roll speed smoothly with the longer gears...kind of like the longer gears now personally, car is much less busy.
All good, hope same for You. Blessings to You and Yours this Thanks!