Visiting india

Hi everyone I'm thinking of visiting india during my summer break in June/July and I was hoping to get some info. When is the best time to book a tour to visit the taj mahal and agra fort, also are there shops that allow you to hire an indian outfit for the visit. Are there any places along the yamuna River where you can have coffee/snack. I'm also keen to visit some of the other mughal tombs, the lotus temple, India gate, qutub minar, rashtrapati Bhavan, museums and the jama mosque. When visiting these attractions is it advisable to have a guide. Is it advisable to keep cash or would my using my card be a better/safer option. Lastly I am of Indian descent (4th generation) but I can't speak Hindi/urdu would I have a hard time making friends.