It's a reasonable itinerary.

I agree and always think flying back to Delhi makes the most sense. There's no need to spend more time on trains than necessary.

The Agra Jaipur train choices include a first class seater, which is quite nice. Given the amount of time you have, I would actually take out Jodhpur and devote an additional day or two to Jaipur. If you just add one day to Jaipur, spend an extra day in Delhi.