Surrendering GC and IRA?

[TN Holder]

Hi,
I am a Canadian citizen holding a valid green card for the last 2 years (I was on TN for 5 years prior), I have left North America since beginning of Jan 2011 to work and live in another country with my family.
I was told by the US immigration officer on my recent entry (first entry after departing US in Jan), that I have to either surrender my GC or get a re-entry permit.

My belongings in US are:
• A rental property
• IRA – which I stopped contributing since Dec 2010
• 529 for my daughter (dual US/Canada citizen), still contributing.

In case I choose to surrender my GC (which I should):
1- What will happen to IRA and 529 accounts after surrendering green cards?
2- Will I be still eligible for world income tax exemption (~$91000) for the first 9 months of 2011?
3- Should I use 1040NR or 1040?
4- Can I still keep the property and continue renting it?
Thanks