Hi,
To do before the two companies are one, last week I transferred $100k of my roth at tdameritrade to Schwab and as a new Schwab customer and with a referral code, they will add $500 of good roth money into my account in 90 days. The money has to stay in the account for awhile, didn't notice how long. Tdameritrade doesn't charge a fee for partial transfer. When they do become one company, probably will be 2 accounts.
Not a new promo, but I wasn't sure if they would honor it from tda since they are buying tda, and they did.
This link has info about the schwab promo and also a promo code that worked for me:
https://www.moneysmylife.com/charles-schwab-promotions/