They don't take possession until 24-hours after closing, so delaying the closing just delays their possession.

If the projects goes south, I take possession of the property or get paid first if they sell it out right. 

Once they are gone and you have possession back, send them a certified letter with detailed list of all outstanding expenses minus their deposit.

Once the new owners takes possession... the taxes won't be low anymore.

So the they will trash the place when they move will be documented as to before and after your possession  starts. 

Does anyone have any information or tips on how to file an ejectment, take possession, insure the home etc. 

The unit is not yours until the tenants have "returned possession" to you.

banks have to hedge to ensure they dont lose money when rates go up. hence they charge for rare extensionon new constructions its preferred not to lock rate until its ready for possession. if you dont need to pay for rate lock extension if you walk away, suggest you go with new bank. 2 weeks is too short for a large bank to get ur loan ready to close.

Do the banks that take possession put them up for sale during the pre-foreclosure period and then if they don't sell ..they go to auction?

Since they left furniture behind they could claim they didn't actually move out and you unlawfully took possession.