It looks very much like the 2 welds on your pipe is where the catalytic converter is placed. My exhaust is different to yours but I took mine apart and inside the down pipe there is another pipe which is slightly smaller which is prehaps some form of restriction but the real restriction is in the can / silencer; there are 2 plates inside with 1 small hole in each one (about 1 or 2 cm) for the exhaust gasses to squeese through, I would assume that your's is simula to this.

The pipes comming from the air box are for the SAI valve and the crank case breather, the SAI valve injects air in to the exhaust to burn off any unburnt fuel and thus reduce emmisions and the crank case breather exhausts combustion gasses that leak past the piston rings. You can simple tie off these tubes out of the way where rain is unlikely to get in to them and prehaps secure a piece of cloth over the end of each one as an air filter. The crank case breather only blows gasses out and the SAI valve does not suck air through anything critical (I think) so they do not need propper filtering.