Firstly, take a deep breath and try not to worry. If you’re on a guided tour you’ll have loads of support when you’re there and they will be used to helping out with all of the queries you’ve listed.
November is a nice time to visit the north of the country and the temperatures won’t be crazy hot. If memory serves me maybe maximums of 30degC and cooler in the evenings and overnight so you may need to light jumpers / fleeces etc.
Currency - yes you’ll need to exchange when you arrive. But that’s straightforward in any major airport. Lots of options, just take undamaged £20 and £10 notes. It’ll take you 10 minutes to do this on landing.
Phone - personally I just sort out an e-sim in advance using Airalo. Depends slightly on what sort of phone you have and how comfortable you are with tech though. It is very easy to buy a sim when you arrive and your guide will be able to help you with this.
I imagine you’ll be in the best available trains / hotels so I’m sure the toilets will be fine. As I mentioned before I would strongly suggest you just avoid meat for the duration of the trip. The veggie food is plentiful and truly delicious. I never miss meat. And yes, avoid washed salads and of course tap water etc.
Finally the visa. The Indian system is quite notorious and it takes a good hour or so online to apply. You then hear back within 72 hours after paying the fee. You’ll just need the tourist visa which is pretty cheap. This is the website:
https://indianvisaonline.gov.in/evisa/tvoa.html don’t be fooled into using any intermediaries. I’ve just used the website for a business visa and I received approval with 12 hours. Just do this a few weeks before the trip.
You’ll have a great time. Your guides will be great and will provide lots of support with all aspects of the trip