Looking to improve over all, i ended up maining him on accident following a string of horrible games and hes been my go to as of now. So Susan mains just drop your insights of match ups and prefered builds and rune paths for those encounters maybe we can bring the doge from a t4 to a t2
Ok. 
You generally want to go up against tanks and melees with lower damage early so you can just farm
Some basic tips that you probably already know, but are important nonetheless.
Respect the enemy laner no matter who they are, because Nasus does have the worst lvl 1-5 experience in the top lane, and possibly the whole game. Still, your passive means that you will be able to stay alive for a long time, even if the auto attacks serve no real purpose on the minions you're hitting.
Because of the top, it's generally good to not use you E to push a lane to increase your chance of the enemy minions pushing to your tower. You're not squishy, so tower dives will be dangerous for the enemy, it makes it harder to get ganked, and it'll actually make it easier to get your stacks. If you feel like you're being overwhelmed by the minions, then that's when you should push it with your E.
If you're using Grasp for you Keystone, I often like to use the auto-attack reset of the Q to proc it off on the enemy laner. Gives you a good trade and the heal. Stacking gets easier as the game goes on, so you can afford to do this as long as you don't stop farming properly. These occasional trades is also how I test the waters as I get my stacks and my sheen. If you find your Q is really hurting them, that's when you can start getting more aggressive.
For runes, I'm boring and use what most use anyway and go Grasp, Demolish, Conditioning, and Overgrowth, with Footwear and Cosmic Insight as secondary runes. Demolish will make destroying the second turret feel like your smashing it with the first tower, and Condition and Over just gives you extra late game defense. Insight is very helpful early since more cooldown reduction means more Qs, and more Q means for stacks.
For items....honestly, your match history tells me you've got the right idea for it already.
For match-ups, I'll let you ask for any specific ones since this is long enough already.
Watch any of Trick2G's Nasus games. The guy is ridiculous as Nasus, Udyr, and Volibear.
Ima just put down a build by psychopathic top thhe only challenger nasus he goes conq with ghost flash every game with the triforce build and he bans darius im p sure.
