With regards to the T4RSP I received, will Box 27 (for HBP) be used to report on Schedule 7? Is that all I need in the software to declare the Home Buyer's Plan to CRA?

Reporting a withdrawal from your RRSP under the Home Buyers Plan is included in the T4RSP slip and no other information is required for your tax return. If you qualify for the First Time Home Buyers Tax Credit you will need to make this claim under the "Deductions" tab and "Payments Profile".

Do i qualify for the credit if the home purchase was completed in jan 2018 even though the HBP withdrawal was in 2017?  Or would i have to wait for the 2018 tax return year?

You will need to wait until 2018 for the tax credit claim.
You can claim $5,000 for the purchase of a qualifying home in 2017 if both of the following apply:
you or your spouse or common-law partner acquired a qualifying home; and
you did not live in another home owned by you or your spouse or common-law partner in the year of acquisition or in any of the four preceding years (first-time home buyer).