What Revisions Should I be Making to my W-4 upon Purchasing a home; also how to make use of the MCC credit I opted into on the form?

You probably should not make any changes to your W-4 in the year of purchase. In most cases the tax savings will be minimal. It's usually best to leave well enough alone until you file the return for the year FOLLOWING the year of the purchase. By then you will have a good idea what the tax impact is and can adjust withholding much more accurately.

No way to say what the impact of the MCC might be without a lot more information. See the instructions on Form 8396 https://www.irs.gov/pub/irs-pdf/f8396.pdf for more information. Keep in mind that if you sell within 9 years, some of the credit may be subject to recapture. See IRS Pub 523 https://www.irs.gov/pub/irs-pdf/p523.pdf and IRS Form 8828 https://www.irs.gov/pub/irs-pdf/f8828.pdf and the 8828 instructions https://www.irs.gov/pub/irs-pdf/i8828.pdf for more information there.

There is no Head of Household status on Form W-4. It's merely an additional withholding allowance IF you qualify to file as HoH. Your mortgage has nothing to do with HoH filing status, so if you were not HoH before you bought, you still are not HoH.

HoH is a filing status for someone who maintains a home for a closely related person such as their child or an elderly parent. See IRS Pub 501 https://www.irs.gov/pub/irs-pdf/p501.pdf for more information on the various filing statuses and the rules for each of them.

a tax accountant should be consulted

"Head of Household" has nothing to do with buying/owning a house. It is for single people who are supporting other qualifying individuals.

Otherwise, there is not much that anyone can do here.

Your best bet is to make an appointment with a tax professional and run the numbers.

You speak with an accountant