New Construction. Lender Choices and Commission Rebate - Zillow

Hi,
I'm trying to do a new construction through a builder in Dallas in their community.
The builder would give me 3% incentive for using their mortgage.
and i'm also getting 2.5% commission from my realtor.

Now can i go with a different lender( who is paying my closing cost) and apply 2.5% realtor's comission towards design center upgrades? I didn't sign any contract yet.
For new construction, would any lender charge me interests through out the building process which is close to 5-6 months?

Thanks in advance.

Source: http://www.zillow.com/advice-thread/New-Construction-Lender-Choices-and-Commission-Rebate-Question/463668/

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