What advice do you have for someone who justed signed up to be an infantryman in the NJ National Guard?

There is a ton of opportunity right now in the ARNG. As an AGR BN Training Officer I have more schools money than I can spend. If you have aspirations of Air Assault, Pathfinder, Ranger, etc. now is the time to go.

As far as a culture shock, its heavily unit dependant. Its been my experience that discipline is pretty tight in Combat Arms units. We've discharged the majority of the HT/WT and APFT failures in my BN. The support units are typically where I've found the stereotypical Guardsmen at. I'm sure there are ate up infantry units too though.

Finally, be prepared for the challenge of managing two careers. You will be expected to maintain your fitness on your own. As you progress in rank there will be an increased amount of time you'll need to spend outside of IDT to be successful. Finding the balance between your day job and the ARNG will be key to your overall success in both of your careers.

It looks like you're coming from Active Army to the Reserves/Guard.

This is highly dependent on the unit you're assigned too, but don't expect military customs, ext to be anywhere near as prevelant as in AD. You may even see overweight soldiers that have no place being there.

However, you will meet guardsmen that come from a variety of backgrounds and skills completely different to their MOS.

As an infantrymen, expect to be among the first called for natural disasters, riots, ext.

I think you're already ready, just in asking the question. Get proficient in everything that is required, class work will give you the insight, then you'll have to take it from there, "All the Way".
Once 11-Bush, aim high, I did as a PFC, get the EIB.