I've been playing for about 6 months and am really trying to understand all of the inner workings of my marker also with its accessories. I'm a little confused or puzzled about 2 different accessories. I'm curious about expansion chambers and low pressure kits. When it comes to the expansion chamber, do I need that with N2 or just Co2?

Expansion chambers are used with CO2.

Why would I need or want a low pressure kit?

Reduced operation pressure results (supposedly) in decreased sound and increased accuracy due to consistency.  (I have never been impressed with them on Tippmanns.)

Is it for tanks that are rated for a higher pressure?

No.  The term "low pressure" refers to the operating pressure of the marker.  In the case of the Tippmann kit it decreases the standard output of a high pressure regulated tank (approx. 850 psi) down to the low pressure range (approx. 450 psi).

If anyone could help I would appreciate it. Thank you for your time.

p.s. I'm not sure if it matters, but I'm mainly a woodsball or scenario player.