Since you aren't permitted to stay the night in the Park, Ghangaria will be your best option. It has a Forest Rest House with clean rooms and all the basic amenities. You can book at the Garhwal Mandal Vikas Nigam (GMVN) website.
Pin Parvati was my first 5000 m climb. Although I was mentally prepared for the distance I'd be covering, I was quite nervous about it despite my preparations.
4 months prior, I started carrying my backpack (almost 12kgs) around an uphill route to strengthen my back. Along with a few 7km runs, climbing stairs and strength training, I worked towards building my endurance.
The trek was a tough one, but I was quite happy with how this paid off. I hope this helps whoever it may concern! :)
As we trailed through the Valley of Flowers, our guide led us to the Khunth Khal ridge. He showed us a rare Himalayan flower found in the park, the Brahma Kamal. The flower has been declared endangered, even so it has a blooming presence on the ridge. If you are here in the monsoon, do not miss this beautiful sight!