Question regarding high charges vs. credit limit on card

I have a personal credit card that I use to charge business related expenses, and a few personal expenses from time to time. Usually for personal expenses, I have a debit card, and I just use my phone and transfer cash to the debit card for my personal purchases. I'll open a card up at a store to save 10% off, but will then make the payment in full and cancel the card. I use my credit card at restaurants even when it isn't business related because I never let my debit card leave my sight or possession.

My credit score is good, 726, but it should be better. I just ran a credit and score report. I show my mortgage, a Home Depot card with a $10k limit and no balance, plus a Best Buy card with a $5k limit and no balance, and then I show 23 other credit cards that have been opened and closed, all cards like Sears, Kohl's, Macy's or something like that where they offered a big discount to sign up for their card. I have no car note, either.

We are considering purchasing a new home and want to squeeze out more points in our scores before we submit anything, so we can obtain the best rates. I'm wondering if how I handle my business transactions has been having a negative affect?

The card I use for business expenses is a Merrill Lynch Platinum Plus Cash Back Visa. My interest rate on the card is under 9% fixed, not variable, and I've had it for well over ten years. When the Great Recession hit, and all the banks were cancelling cards or raising interest rates high to get people to drop them, Merrill Lynch kept this card steady at like 8.89%. I have a $20,000 credit limit that I've had on there for the last eight years. I haven't asked to raise it. Most months I will charge between $10k-$17k on business expenses. My company reimburses me every week, and so I'm never behind on funds and I pay it off every month.

The question is, since I never have a balance except my current charges, is that a positive or a negative? Also, since every month I use between 50% - 85% of the available credit on that VISA, does that negatively affect my score?

Would I be better off adding one or two more cards (AmEx, Mastercard), then split the charges among those cards to keep a lower charge to credit ratio? Conversely, by adding the extra cards does that take my credit score down, negating the point of adding them in the first place?