Katherine, I agree with Walesmaven. I think it is a good idea to operate a separate account for your shopping, but for a different reason. The balance I keep in my shopping account I refer to as my 'shop kitty'.
I hate using household money to do shops and then trying to remember to put it back in 'household' when I get paid and reimbursed. The 'kitty' account allows me to pay the credit card charges due to shops from the 'kitty' and pull a little cash for those shops that require cash payments. When the 'kitty' gets too fat, I move the money over to 'household'.
I definitely use my normal credit cards for shops because of the cashback bonuses that I accrue over time. And because the 5% cash back deals change month to month, I carry a variety of cards. For May, for example, the 5% was on the Discover card for groceries, restaurants and movies. My business put about $300 on my Discover card in May, which is only $15, but over time mounts up nicely. Since over the course of a year I am likely to lay out $5000 to $7000 on shops to be reimbursed, using the card with the best bonus for that type of establishment for that month works well for me.
I applaud you looking at accounting information to get yourself set up and started. Single entry bookkeeping will do fine for IRS purposes and it is primarily IRS that you need to satisfy. They are going to be happy enough with any contemporaneous record keeping that is easy to follow and complete. My personal choice is a Excel spreadsheet that has dates, jobs, addresses, mileage, company I did the work for, fee, bonus, reimbursement, date paid and amount paid. Paypal and bank records can show the relevant receipts. Credit card statements (highlighted for those charges that are shop related) and copies of the receipts submitted for reimbursement show the outflows. Receipts from oil changes on my vehicle help support my overall mileage claims, while a quick visit to Google Maps or similar can support a specific mileage claim for a shop or a route. Even the simplest of consistent record keeping will go further in protecting you that you are indeed a small business than having or using a EIN.