@RaraRachaelWhat you are proposing is a well trodden tourist route. However I would never ask a loval travel agent to do it. India is very chaotic and I’d make absolutely sure all arrangements are watertight and do not stay in cheap hotels.
First things first. You need a car with a driver to take you to the hotel. The tour operators like Audley will do this for you. Then, what are you going to do in Delhi? You will find it much easier to have planned pre organised tours. They will collect you and guide you for the day or half day.
You then need transport to Agra for the Taj Mahal and then need transport to it from your hotel. It will be busy. Check out other things you can do. Food tours are popular.
I’m assuming you will visit Jaipur as it’s the closest city to Ranthambhore NP. You really need to see Jaipur or it’s not the golden triangle. There is good shopping, a palace and the Hawa Mahal to visit and you could even stay in a palace! There’s plenty to see here but you need a guide as there’s a degree of hassle.
Lastly Ranthambhore. I’ve been twice and it’s changed SO much! In the 80s we were the only tourists! Had the park to ourselves and saw tigers. Went back in around 2008 and it was manic. They only let so msny vehicles into the park and there’s total chaos at the gate. You need to get in! There’s now a huge array of places to stay and the park is, essentially, overrun. We did see a tiger in 2008 but there were big lorries taking many people round and it was noisy and the vehicles could be heard coming. Not sure I would bother. It’s hugely attractive but has serious flaws for wildlife viewing. Other parks are much better but not easy to get to.
The hotels are your haven from the noise and chaos outside. You don’t need to be fit. You need a certain sense of adventure and I cannot remember smells but you don’t visit tarpaulin city so don’t worry! It’s great weather in our winter.
I have been to southern India but distances are much greater between sights. I’ve also travelled on Indian trains - smells aplenty in the loos. Avoid. Get a driver with a 4x4. Realise the roads are full of animals as well as vehicles and you do need a high quality tour operator to be certain you are safe and taken care of.