New PLLC in NY

On the tax return NOTHING changes ... the business is still reported on the same Sch C ... the only thing you will do is ADD the EIN to the Sch C form. 

You will need an EIN which is easy to get and FREE :  https://www.irs.gov/businesses/small-businesses-self-employed/apply-for-an-employer-identification-number-ein-online

And you should NEVER use a personal checking/credit card  account to pay for any business expense or accept any income for the business.   If you do and the IRS  audits you then you will find yourself "in a never ending nightmare" as Carl would say ... this is not a good business practice ... and if you are going to be in business you have to act like it.   I recommend you sit down with a local accountant and get educated on the business of running a business. 

. Here is some reading material……

IRS information on Self Employment….
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Self-Employed-Individuals-Tax-Center 

Publication 334, Tax Guide for Small Business
http://www.irs.gov/pub/irs-pdf/p334.pdf 

Publication 535 Business Expenses
http://www.irs.gov/pub/irs-pdf/p535.pdf 

Home Office Expenses … Business Use of the Home

https://www.irs.gov/businesses/small-businesses-self-employed/home-office-deduction

https://www.irs.gov/pub/irs-pdf/p587.pdf

I an transferring from a non-incorporated sole proprietor Schedule C to a single-member PLLC still filing a Schedule C as a disregarded entity (sole proprietor).

Actually, you are not transferring anything what-so-ever as far as federal taxes are concerned. You will file the SCH C "as if" absolutely nothing changed, because the fact is, "nothing changed" as far as your federal taxes are concerned.

Do I have to do anything to "close out" the old Schedule C and transfer to the PLLC?

There's nothing to "close out" and nothing new to open. It's basically "business as usual" and that's pretty much it. But there are a few important things that matter here.

it seems I have to get an EIN to open a bank account to deposit business checks

It's a fact that a vast majority of banks (and I don't know of any exceptions) absolutely *require* an EIN for any type of business account. Now understand that the IRS is the only authority that issues EIN's and that's it with no exceptions. The EIN "must" be tied to the owner of the business. So it's "IMPORTANT" that when applying for the EIN that you do so with the same exact social security number you've been using for the business on the SCH C in the past. Otherwise, you will end up with a reportable (and possibly taxable) transaction of transferring the business from one owner to a new owner.

although I intend to continue paying for expenses out of my personal account,

Bad, bad ***BAD*** move on your part. That makes it almost impossible to keep business transactions separate from non-business transactions. If audited you will find yourself in that "never ending nightmare" I'm known for referencing, and you *will* lose.

Get that business account open yesterday, if not sooner. Then transfer "EVERY" "SINGLE" "PENNY" of income earned by the business in 2019 into that account. That amount you transfer will be your "GROSS" business income thus far in 2019. (I hope you have the cash to do that with, too!)

Then from there you can transfer back (the next day or after) those business expenses which you can prove with a receipt in a court of law, were paid by the business and solely "for" the business and business purposes.

Every single penny of business income, as well as every single penny of business expenses *NEEDS* to be run through that business account... and you *only* run business money (income and expenses) through that account. That's it, and nothing else.

Then you set up periodic withdrawals for once or twice a month (or whatever you want) for you to take the profits earned by the business, for your use as desired. Those withdrawals are referred to as, and labeled as "owner's draws".  THere's two basic types of owner's draws and correctly labeling the withdrawal is important - especially if using Quickbooks to help track business income and expenses. (Which I highly recommend.)

Owner's draws - Withdrawal of Capital -- This is a withdrawal of money that you used to start the business. When deposited it was referred to and labeled as "Owner's Capital Contribution". That initial start-up money was money that you already paid taxes on - possibly in a prior year. A "withdrawal of capital" is not a withdrawal of taxable income, because all you're doing is taking out the money you put in to start the business. You paid taxes on that money already so you don't need to pay taxes on it again in the tax year you take it out. If this type of transaction is not properly labeled for what it is in Quickbooks, then your balance sheet *WILL* *NOT* *BALANCE* with your tax return at the end of the year. I guarantee it.

Owner's Draws - Note that this type of withdrawal has no sub-category to break it down further. This is a withdrawal of taxable profits earned by the business. It is not a withdrawal of any of the initial business start-up capital.