With regards to headers; keep in mind that jdm spec headers (such as toda) will not bolt up directly to the oem cat and catback... It's been covered on here a lot before if you want more info but basically if you do try and put jdm headers onto stock catback you will have to either use the audm cat converter and but a bit off the stock catback, OR use a jdm cat converter and weld an extension onto the catback....
Here is one of the threads with more info, made by Rhys up here in brisbane :)
http://www.ozhonda.com/forum/showthr...st-differences
Concerning noise, I recently installed toda headers, high flow jdm cat and fujitsubo rm01a... It is definitely louder but there is no droning sound like with a lot of setups... Combined with my injen intake the vtec sound is absolutely awesome :D
And about oil, I have used penrite sin 5w-60, nulon full synthetic 10w-40 and am currently using penrite ten tenths racing 10w-40... As long as you go full synthetic you really can't go too wrong so just read around and make your own decision at the end of the day... You'll probably change it in 5000 kms anyway so experiment a bit and find one that works best for your car... :)
All the best with the new car, congratulations on the purchase!