I ride with my brakes switched also, not a big deal. it should be relatively easy to do.

With the seatpost, were you looking into a suspension seatpost or a seatpost made of a material that is more forgiving? I really don't think you'll be able to find a nice steel seatpost, just a really crappy cheap one. You said you didn't think carbon would be ok....what kind of riding do you do? XC, downhill? If xc, it sounds like you are more petite, so I really don't think a carbon seatpost would be an issue for you. I currently have a carbon handlebar and have had no issues at all wtih it. Another option you may want to look into though is Ti. Moots, USE, Dean are a few companies that come to mind for a Ti seatpost.