how often are you planning on going to the dunes? if you are just going to go once or twice a year then i would just get a cheap set of paddles. why spend big money on paddles if you are never going to use them. now if you think that you are going to go to the dunes alot then you might want to look into a better paddle.
for jetting... i just call the manufacturer of the pipe (toomey, PC, fmf, etc.) and tell them what mods what elevation and they give me a ball-park jet. then you can go from there. also there are some jetting gurus on here that can get you pretty close.
stock silencers already have a spark arrestor.