Can anyone advise me of where to get the bus schedules online and also where I can purchase tickets (bus, train, etc.) before I go?
Sorry...the. Cotswolds
We have mostly used trains (BritRail pass), but have used buses on occassion. We don't purchase in advance.
National Express is the company that services the major centers in the Cotswold with bus service. You can find advance-purchase deals on some fares there.
For train travel, walk-up fares can be expensive. If you know your travel dates, you can get excellent deals on advance fares. The cities in the Cotswolds are served by several train lines, but the best one to order tickets seems to be the National Express rail website. Its site seems to have been the most accommodating in the past to accepting American credit cards without requiring a British address, etc. As you will see, fares from, say, Gloucester to Oxford range from 6 GBP to 41 GBP!! So if your journey dates are fixed, you can save a lot by purchasing in advance.