I did a January departure for the OAT "Heart of India" tour. Like you, my tummy doesn't tolerate ****y foods very well. At every meal there were enough alternatives that I had no trouble finding appropriate food. The desserts will add pounds!! Breakfasts are quite nice, especially with wonderful fruits and teas available. At one lunch I was a bit dismayed because I couldn't find anything on the buffet I could eat; then I was directed to the OAT sit-down meal featuring more convention Western cuisine. The last night we had a Western style dinner with fried chicken and fried fish, mashed potatoes, etc. with plain ketchup and tartar sauce. The wait staff thought it comical that we could enjoy such bland fare. It was a banquet to us. The weather was perfect; mild weather and very little rain. Some of the compounds where you will stay are magical places, real paradises from the teeming masses outside the walls. The contrast is staggering.
As for the long bus rides. There were a couple of those; however, you see so much of how the people actually work and live. The guide will point out many interesting things along the way. You will be astonished at almost every turn. Keep you camera and journal at the ready.
Vendors are very much in evidence at the tourist locations. Our guide controlled them by not allowing any vendors on the bus. He held up each item they were hawking. Anyone who wanted it, bought it; none of us had to be pressured. If people buy things on the sidewalk, they are mobbed by all the vendors. It can be overwhelming for timid individuals, especially if they are alone. Visiting India is quite an adventure. Be ready for the culture shock and the crowds. Have a good time.