New 2007 M35x owner. Need advice!

[USMC5811]

Hey guys, I just bought a 2007 M35x last week, and so far I love it! I've been searching through this forum for days now just trying to gather as much knowledge as I can. It's bone stock right now and has 79,000 miles.After researching certain topics for hours, I still can't find the exact answers to certain questions I have, and quite honestly I'm getting sick of reading so asking a few specific questions will alleviate all of that lol. Just so you know what I'm going for, I'll briefly describe it. I baby my vehicles, and I'm not a nascar driver, so I don't care how fast it is. I'd love to improve gas mileage with easy add-ons and/or maintenance if possible (I'm not complaining about gas mileage, I traded in an Escalade EXT lol).I just want to start off on the right foot with the car and make sure that it runs forever! Now for the questions...finally

1. I've read a lot about changing the PCV, and mixed reviews on using aftermarket. Can I use aftermarket? What's my best option?
2. I was looking in to intakes because I feel as though it gives the vehicle a much better tone, as well as increase power and sometimes MPG. Does anybody have any suggestions? What are the reasons for your suggestions? Or is it better to just drop in a K&N filter?
3. WTF is a plenum spacer, and why are they raved about so much for our cars? What will it do to my performance/MPG?
4. I've also read a ton about all of the different types of tunes. If it's strictly for performance then it's not necessary for me. However, if it helps the vehicle run better and last longer, then I'll do it.
5. I love the look of the 08 sport bumper, from what I've gathered all I need to buy is the bumper and the grills correct?

I'm going to flush all of the fluids, change the oil (using only synthetic from here on out), and replace the plugs (with NGK) within this next week.Keeping in mind that I don't want to sacrifice the reliability or the durability of my engine, which mods should I get to help her run better for longer? I don't want to add or modify anything that could potentially cause a more than normal pattern of wear and tear. Thanks in advance for everyone's help, I'll be an M35 pro in no time, until then I know nothing, but I know everything about Escalades if anyone needs advice haha. Thanks guys.

[dsoccer413]

Just bought a 2006 M35x, saw your post here, over a year ago. Did you do anything and see any improvement?

[rxmclaren7]

hey sorry no one responded to your post for over a year USMC5811!! if you are still in the market for a K&N filter i have a lightly used one that i would be willing to let go...for a Veteran ( i assume you are with a name like USMC5811) all i would ask is for you to give it a good home...that means no charge!