Air filter... Any seasoned off road person I know (bike or 4 wheels) avoids a fabric filter like K&N for dusty or sandy off road conditions. Sure they flow better but there is a reason and they just can't trap fine dirt as well as a properly oiled foam filter. I like the Uni. I left the top on the airbox but I added a sheet of Uni filter element (green fine filter) that I cut to size and put it over the filter as a prefilter - it is very easy to clean that way and don't have to clean the main filter which is harder. Works well. Obviously I'm not trying to achieve maximum performance. I'm happy with the performance and want to maximize fuel mileage and engine filtration/protection and keep it simple to maintain.
You can use a biodegradable oil like NoToil or J&P or Yamaha or whatever and clean it up with a filter cleaner and water in a sink in your hotel room. Safely. I use NoToil spray oil and clean it with a little bit of powdered Oxyclean in a small 5 quart plastic bucket with warm water. The days of using gasoline to clean it are over! finally.
I think Leafman is one of a very few who like the 17 sprocket. I'm frankly a bit shocked by that and I'm willing to bet most offroad people like to go down to the 15. It just depends on how slow you ride in first gear and how fast you ride in 5th gear. When I'm crawling up slickrock in Moab I have even used a 14 tooth for a short trip. I'm happy going 80mph on a 15 but hey we all have opinions.
Exhaust... Forget the Akra, crazy prices. For me the Leo is still working fine, you just have to beef up the mounting system at the top of the muffler so there is no way it can sag and melt your coolant hose at the front of the pipe. See my mods page for ideas, there are other better ideas out there.
Auxiliary lights... People seem to love HID lights. I went the opposite path. I wanted LOW current draw, reasonable light output and CHEAP. I went with 2 of the modest model 30 LED lights from sanjoh at AdvMonster.com for $60 each or so... and you can read my Aux Light MOD for more details. The early models sanjoh sold reportedly had quite a few failures. I personally believe this was due to running the drivers at a very high current to achieve the most light output. My solution to this is to also install his $45 LED Dimmer module which is waterproof and has a wireless remote control fob. It also has a high beam bypass control input that I wired to my high beam so that when my high beam is on it always outputs 100%. The beauty of this is you can aim the light for proper location for high beam but set the dimmer to only output say 30% when you are in low beam mode, so in daytime cars can see you a bit because they are on and aimed a bit high but it does not stress the lights at all running at this low PWM duty cycle. In this "low" mode I measured the current draw at only 0.25 amps for both of them! Then hit the high beams at night and WOW they are bright! When both of them are on 100% I measured them to pull only 1.4 amps. That's the equivalence of each one being 7.5 watts!
I've had them on a year now and no problems at all.